In recent years, if you bought shares in Cisco Systems Inc., Dell Computer Corp., Intel Corp., and Microsoft Corp., you saw nothing but gains over time. It is difficult, in fact, to think of a better set of large-capitalization bellwethers to have held in your portfolio from, say, 1994 to 1999. Microsoft alone saw its shares zoom skyward 16-fold between 1994 and its high in 1999. Dell shares multiplied in value 93 times from late 1994 to March 2000. Intel shares magnified in value almost 20 times over a similar time period. Over the last decade Cisco's share-price appreciation topped that of nearly every company listed on the Nasdaq. 2000 has been a different story. Dell, Microsoft, and Intel lost roughly half their value over the last six months. Cisco shares as of mid-October were up only 5% for the year. Microsoft alone shed a quarter of a trillion dollars in market capitalization. Part of the reason, of course, is that the broader tech market has fared poorly. Then there's the fact that three of these companies suffered some kind of setback that caused Wall Street to withdraw their golden status. But the broader, longer-term reasons are that their traditional markets are changing, and they face new competition. Take Cisco, for starters. Since March the company has lost nearly one-third of its market value. Meanwhile, shares of Cisco's hottest competitor, Juniper Networks Inc., have appreciated 300% this year. Two other competitors, Extreme Networks and Network Appliance Inc., have seen their share prices nearly triple this year. Dell's problems go back to last year. In late 1999, Dell warned investors that its earnings would be below analysts' estimates. And again on Oct. 4 the company said its revenues for the third quarter and profits for the fourth quarter would fall short of targets. Also hurting Dell's prospects is Wall Street's sense that the market for $2,000-plus personal computers is being eroded by the incursion of all manner of Internet-connecting devices. Intel's troubles are well known. Even if the company hadn't announced softness in its European sales, triggering a loss of $90 billion in market capitalization, its share price still looked bloated, according to some securities analysts. The big problem, they say, is competition from strong competitors such as Advanced Micro Devices Inc. and several Taiwanese firms. Another problem for Intel is that, as CEO Craig Barrett admits, "Eighty percent of our revenues are tied to the personal computer." Thus if, as many have predicted, the PC market enters a period of low-, zero-,or even negative growth, Intel's dependence on sales of chips to PCs becomes a weakness, not an advantage. Barrett says Intel plans to tap the networking and telecommunications markets that offer stronger growth potential. That brings us to Microsoft. While the government's antitrust ruling against it awaits a lengthy appeals process, the company continues to go forward with a giant-economy-size pair of handcuffs about its corporate wrists. With the feds scrutinizing Microsoft so closely from their Washington Beltway guard towers, Gates & Co. doesn't dare attempt a single acquisition of any significance. Sure, the company continues to take equity stakes of $10 million here and $30 million there in companies whose technology it would like to own. But don't look for the earthshaking AOL-Time Warner-size deal that could push it to the next level. Further weakening Microsoft in recent months has been a steady drain of top talent, including several key executives. Finally, there's the gathering threat of Linux and other so-called "open source" software that's a heck of a lot cheaper to purchase than Windows 2000 and its brethren. Now, some may point out that these stocks have simply mirrored the movement of the market in general, and that the investment winds of 2000 have blown poorly not only for them, but for the majority of technology companies as well. Viewed in that light, Cisco, Dell, Intel, and Microsoft are still the bellwethers they once were. I have a hunch, though, that underlying this once-bulletproof quartet's slide are shifting markets, a spate of new competitors, and the Street's sense that their days of dominance may be numbered.