The losses combined with higher volume constituted a distribution day for all major indexes. The Nasdaq suffered its third distribution day in the past seven sessions.

The sudden spate of distribution days and weak action among many leading stocks indicates that the market uptrend is under pressure.

Raising some cash would be prudent under this condition, and raising your standards for possible buys would also be wise.

The bull market that began in March 2009 is now at the 21-month mark. It's natural for old bull markets to develop more choppiness.

History shows that bull markets starting in the wake of a severe bear market will rise about 20 months before running into trouble. Often that trouble shows itself in choppy, sideways action

Chinese Internet content provider Baidu, which has been a leader since the Sept. 1 follow-through, dived 6.42 to 100.20 in fast trade. The stock also pierced its 50-day moving average. Baidu recovered from a similarly big loss on Nov. 16, but that drop didn't undercut the 50-day line.

Wednesday's loss was Baidu's biggest percentage drop and price drop since June 29, when the stock fell 6.87, or 9%, in big volume. That move established a short-term low, but circumstances were different. The Nasdaq was then near a low, not a high.

Is Wednesday's action a signal to sell Baidu? It depends. If you bought recently and are up 20% or less, it may be prudent to protect your gain. But if you have a larger price cushion, the decision is less pressing.

Baidu isn't alone in encountering head winds. A number of leaders (or former leaders) have seen price erosion in recent weeks.

Meanwhile, Investors Intelligence's bulls vs. bears survey remained at a level sometimes associated with market tops for a fifth consecutive week. The contrarian gauge is a secondary indicator, meaning it isn't as reliable as the price and volume action of the market itself.