Michael Morris and Jeff Lowenstein wouldn't have recognized each other if they'd met on the street, but that didn't stop them from getting into a shouting match. The professors had been working together on a research study when a technical glitch inconvenienced Mr. Lowenstein. He complained in an e-mail, raising Mr. Morris's ire. Tempers flared.

"It became very embarrassing later," says Morris, when it turned out there had been a miscommunication, "but we realized that we couldn't blame each other for yelling about it because that's what we were studying."

Morris and Lowenstein are among the scholars studying the benefits and dangers of e-mail and other computer-based interactions. In a world where businesses and friends often depend upon e-mail to communicate, scholars want to know if electronic communications convey ideas clearly.

The answer, the professors conclude, is sometimes "no." Though e-mail is a powerful and convenient medium, researchers have identified three major problems. First and foremost, e-mail lacks cues like facial expression and tone of voice. That makes it difficult for recipients to decode meaning well. Second, the prospect of instantaneous communication creates an urgency that pressures e-mailers to think and write quickly, which can lead to carelessness. Finally, the inability to develop personal rapport over e-mail makes relationships fragile in the face of conflict.

In effect, e-mail cannot adequately convey emotion. A recent study by Profs. Justin Kruger of New York University and Nicholas Epley of the University of Chicago focused on how well sarcasm is detected in electronic messages. Their conclusion: Not only do e-mail senders overestimate their ability to communicate feelings, but e-mail recipients also overestimate their ability to correctly decode those feelings.

One reason for this, the business-school professors say, is that people are egocentric. They assume others experience stimuli the same way they do. Also, e-mail lacks body language, tone of voice, and other cues - making it difficult to interpret emotion.

"A typical e-mail has this feature of seeming like face-to-face communication," Professor Epley says. "It's informal and it's rapid, so you assume you're getting the same paralinguistic cues you get from spoken communication."

To avoid miscommunication, e-mailers need to look at what they write from the recipient's perspective, Epley says. One strategy: Read it aloud in the opposite way you intend, whether serious or sarcastic. If it makes sense either way, revise. Or, don't rely so heavily on e-mail. Because e-mails can be ambiguous, "criticism, subtle intentions, emotions are better carried over the phone," he says.

E-mail's ambiguity has special implications for minorities and women, because it tends to feed the preconceptions of a recipient. "You sign your e-mail with a name that people can use to make inferences about your ethnicity," says Epley. A misspelling in a black colleague's e-mail may be seen as ignorance, whereas a similar error by a white colleague might be excused as a typo.

If you're vulnerable to this kind of unintentional prejudice, pick up the phone: People are much less likely to prejudge after communicating by phone than they are after receiving an e-mail. Kruger and Epley demonstrated this when they asked 40 women at Cornell to administer a brief interview, 20 by phone and 20 by e-mail. They then asked a third group of 20, the "targets," to answer the phone interviewers' questions. They sent a transcription of the targets' answers to the e-mail interviewers.

The professors then handed each interviewer what they said was a photo of her subject. In reality, each got a picture of either an Asian or an African-American woman (in reality, all were white).

E-mail interviewers who thought the sender was Asian considered her social skills to be poor, while those who believed the sender was black considered her social skills to be excellent. In stark contrast, the difference in perceived sociability almost completely disappeared when interviewer and target had talked on the phone.

E-mail tends to be short and to the point. This may arise from the time pressures we feel when writing them: We know e-mail arrives as soon as we send it, so we feel we should write it quickly, too. On the other hand, letters depend on postal timetables. A letter writer feels he has a bigger window of time to think and write.

Psychologists Massimo Bertacco and Antonella Deponte call this characteristic "speed facilitation," and they believe it influences our episodic memory - our ability to recall events. They found that e-mailers wrote shorter messages and were less likely to "ground their communications" in memories of shared experience than letters writers were.

The brevity of e-mail and the absence of audiovisual cues can endanger business and personal relationships unless e-mail is supplemented with the rapport that comes from more personal communication.

"Rapport creates a buffer of positive regard," says Professor Morris, "and when it's not there negotiation becomes brittle, vulnerable to falling apart."

Morris, who studies negotiation at Columbia, led a study that found that negotiators exchange more than three times the information in face-to-face interactions as they do via e-mail. Though Morris and his colleagues concluded that e-mail lets negotiators make "more complex, multiple-issue offers," they ultimately built less rapport, thereby increasing tensions and lowering the average economic value of the agreements.

Rapport "is an interpersonal resonance of emotional expression," Morris says, "involving synchronous gesture, laughing, and smiling together. Once this rapport exists, it's a buffer against a moment in the negotiation when there's some friction." This buffer is hard to develop without speaking over the phone or in person. Those who negotiated by e-mail in Morris's study trusted each other less and weren't as interested in working together again.

But the pitfalls of e-mail interaction were easily overcome by a single phone call. Morris ran a second round of negotiations, all conducted via e-mail, but made half of the corresponding pairs chat on the phone before negotiating - "just for five or 10 minutes," Morris explains, "and the key thing is we told them, 'Don't get into the issues. It's just an icebreaker.' " The result was dramatically improved agreements.

So if you want to buy something on Craig's List, Morris says, "make a brief phone call, even if it's not practical to do the whole negotiation by phone. You can establish a favorable bias with someone and then proceed in a less rich medium, but it's very hard to just get right into the negotiation on a medium that isn't rich."