Tech stocks fell Tuesday morning after Federal Reserve Chair Janet Yellen said their companies may be overvalued.
"Valuation metrics in some sectors do appear substantially stretched—particularly those for smaller firms in the social-media and biotechnology industries," Yellen wrote in a semiannual monetary report to Congress.
This "stretch" was apparent even "despite a notable downturn in equity prices for such firms early in the year," she added.
Facebook, Twitter, Google, and Apple were all down between 0.4 and 1 percent on the day. The Dow Jones industrial average has been basically flat.
Any long-term effect on the stocks remains to be seen. All four staged afternoon rallies to erase some, but not all, of their morning slides.