(CNBC) — U.S. stocks fluctuated on Tuesday, with investors measuring upbeat earnings from the banking sector against concern from the Federal Reserve that valuations on small-cap and high-flying names might be “stretched.”

JPMorgan Chase and Goldman Sachs Group climbed after posting better-than-expected quarterly results. Facebook and Yahoo fell after the Fed, in its monetary report, called valuations stretched for smaller social media and biotechnology stocks. Lorillard declined after Reynolds American said it would purchase its rival cigarette maker for about $25 billion.

We have “echoes of irrational exuberance, but in an entirely different context,” said Art Hogan, chief market strategist at Wunderlich Securities, referring to Yellen’s comments about biotech and social media stocks, and relating them to a phrase used by then-Fed Chairman Alan Greenspan in the 1990s during the dot-com bubble.

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