To be sure, the situations of Bear Stearns and Enron are different in many ways. For starters, just in terms of company stock, top executives at Enron encouraged workers to load up their 401(k)’s with company shares. That wasn’t the case with Bear.

Nevertheless, the rapid collapse of the investment bank’s shares  they fell to about $10 from $70 in around three weeks  offers yet another reminder of the risks associated with making concentrated bets on your employer’s stock, even if it appears to be a blue-chip investment.

Conventional wisdom says company stock isn’t that big a problem now. Thanks to the bear market and blow-ups at companies like Enron and WorldCom at the start of the decade, as well as the Pension Protection Act of 2006, retirement investors aren’t as concentrated in company stock as they once were.

In general, the numbers bear this out. In 2001, when Enron filed for bankruptcy, investors in 401(k) plans that offered company stock held 28 percent of their retirement account in employer shares, on average, according to Hewitt Associates, the employee benefit research firm. By the end of last year, that figure had dropped to 16 percent.

But many financial planners say 16 percent is still way too much to invest in a single stock, let alone that of your own employer. Think about it: $100,000 invested in the Standard & Poor’s 500-stock index would have shrunk to $90,760 since January. But had a Bear Stearns employee invested 16 percent of his money in company stock  with the remainder going into the S.& P. 500  his account would have fallen to below $78,300. This at a time when his job may be in jeopardy.