Nasdaq Stock Market ( NDAQ - Get Report) shares plunged nearly 5% after the London Stock Exchange formally rejected Nasdaq's hostile $5.3 billion takeover bid, calling the proposal "wholly inadequate." The stock is now trading in the red for the year -- a real rarity in the red-hot exchange sector. Shares were losing $1.80 to $34.19.

UnitedHealth Group ( UNH - Get Report) jumped after the insurer predicted 2007 revenue of about $79.5 billion, which would top the Thomson Financial estimate of $77.9 million. The insurer pegged 2007 earnings at between $4.7 billion and $4.75 billion. Shares were up $1.88, or 3.7%, to $52.28.

Morgan Stanley ( MS - Get Report) rose after it shocked investors by saying it will spin off its Discover credit card business. The spinoff idea had been rejected by Chief Executive John Mack as recently as last year. Meanwhile, the broker reported fourth-quarter profits of $2.2 billion, or $2.08 a share, a drop from last year that nonetheless beat the $1.77-a-share consensus estimate. Shares were up $1.51, or 1.9%, to $81.88.

Citigroup ( C - Get Report) lost some of its spectacular Monday gains after an A.G. Edwards analyst downgraded the banking giant to a hold from a buy. Shares were falling 87 cents, or 1.6%, to $54.57.

KBW ( KBW) fell after an analyst with Merrill Lynch began coverage on the New York-based boutique investment bank with a neutral rating, and said Keefe Bruyette & Woods will not remain immune -- as it has thus far -- to equity pricing pressure. Shares were still down 21 cents, or 0.7%, to $28.00.