“I was skeptical that there were effects that were repeatable,” said Gail S. Prins, a professor of physiology at the University of Illinois at Chicago, and an author of the Endocrine Society’s report. But in 2001 she was part of a panel that analyzed dozens of BPA studies for the National Toxicology Program. The panel had its own statistician reanalyze raw data from the studies to find out if the claims based on it were valid.

“I could see there was some consistent data,” Dr. Prins said. “I started thinking, ‘Hmm, maybe there could be something there.’ It was still curious to me. This is not a regular toxicant. It’s acting like a hormone, and hormones can act at extremely low doses. If you think the dose makes the poison, it doesn’t make sense. But if you think about it as a hormone — and I’m an endocrinologist — it does make sense.”

Her lab is one of the 10 that have received government grants under the economic Recovery Act to study BPA. She is analyzing its effects on the prostate in young mice and rats, and also in rats that have been implanted with human prostate cells. The work is being conducted under strict guidelines set by the National Institutes of Health, to make sure that the results of different groups will be reconcilable.

“This time N.I.H. said, ‘You all have to do oral exposures, and we’ll give you BPA from one source,’ ” Dr. Prins said. “We’re all working with one batch. We all have to measure free and conjugated BPA levels in our model systems, and it has to be done in a certified lab so that our data will be more aligned. It does make a lot of sense to go about doing it this way, and it hasn’t compromised anything I’m doing.”

There is no practical way to do these studies except in rodents, she emphasized. “I can’t look at early-life exposures and prostate risk in humans,” Dr. Prins said. “I can’t do it in my lifetime even if I start now. Likewise I can’t take men who currently have prostate cancer and see what their BPA levels were when they were born.”

Over the next few years, researchers hope to bring coherence to this confused and troubled field.

“This is a chemical we’re all exposed to, and I think that makes it incumbent upon us to study it,” Dr. Birnbaum said. “We really need to know what it might be doing, if anything.”