Following Monday's announcement of a 4-for-1 split of its shares, Chiron's common jumped $9.75 (10 percent) in two days of trading to close Tuesday at $106.50. The shares then pulled back to close the week at $104.25, up 8 percent.

In addition to the obvious rationale of making the stock more accessible to retail investors, CHIR said the split would increase liquidity for its institutional holders. "The number of actual floating shares is relatively small for a company of our size," said spokesperson Larry Kurtz. The company has a little over 40 million shares outstanding, but partner Ciba-Geigy owns 49.9 percent of them. On top of that, officers, directors and major investors hold 8-9 million shares, leaving only 14 million or so in the float.