WAL-MART DROPPED THE BOMB last week. It wasn't exactly a nuclear number, except if you happen to be Walgreen, CVS or Rite Aid, whose stocks were more or less pulverized when the mammoth merchant announced that it planned to offer generic drugs at knockdown prices (more specifically, $4 for a month's supply).

From the standpoint of the drugstore outfits -- or pharmacies, as their fans like to call them -- what the world doesn't need is another vendor of drugs. And, as the action in their shares makes painfully clear, the very last thing in the world they need is that vendor to be Wal-Mart.

Our savvy friend Larry Feinberg, proprietor of Oracle Investment Management, which concentrates on pharmaceutical and biotech companies, sees the push by big, muscular outfits like Wal-Mart and Target to cut generic prices as bad news for a number of companies beyond the drug chains. Wal-Mart's thrust, he says, will hit such companies where it hurts most -- in their profit margins, which have been exceedingly plump.

The Wal-Mart disclosure marks, in his words, "the beginning of a period of increasing transparency -- where consumers and those that bear the freight alike will be seeking information about what the true costs of generic drugs are." And, he predicts, the disintermediation that will occur will hurt drug distributors (McKesson and Cardinal Health come to mind) as well as drug chains.

Moreover, Larry thinks the impact will be "devastating" on pharmacy-benefits managers like Medco Health Solutions, Caremark Rx and Express Scripts, some of which in some cases get the bulk of their profits from their mail-service generic drug business.

The decline, he adds, "won't happen overnight. But the die is cast."