Shares of cancer-drug maker Celgene ( CELG) sank after research firm SG Cowen initiated coverage of the stock with a neutral rating.

While Cowen's biotech analyst Phil Nadeau says revenue from the company's Revlimid should reach $2.3 billion in 2010 from $331 million for all of 2006, the drug's success is already priced into the stock, which is "modestly overvalued," he believes. Nadeau says he would look for a pullback before building a position. Shares fell 3.4% to $44.39.

MicroIslet ( MII) fell despite an announcement that the company's transplantation studies on diabetic primates reached a six-month milestone. After jumping early in the day, shares were lower by 9 cents, or 5%, to $1.70.

Shares of medical-aesthetics company Syneron ( ELOS) were jumping 15.6% to $21.39 after the company reported earnings and reiterated its guidance. Syneron's quarterly revenue reached $27.5 million, up 37% from a year ago and was a record high. Overall, the company earned $8.9 million, or 32 cents a share, including stock-based compensation expenses.

Excluding charges, the company earned $11.3 million, or 41 cents a share, in the quarter, up 22% from last year. Analysts were expecting the company to earn 39 cents a share. The company said it was on track to meet its previously announced guidance, which in February called for revenue of between $113 million and $120 million for the full year.

Among other health care stocks on the move were pharmaceutical company NitroMed ( NTMD), which was gaining 14.1% to $2.91, drug developer Taro Pharmaceutical Industries ( TARO), up 7.7% to $12.81, biotech ICAgen ( ICGN), higher by 7.1% to $1.20, and Spectrum Pharmaceuticals ( SPPI), up 3.4% to $3.68.

Accentia Biopharmaceuticals ( ABPI) was down 1.6% to $3.03, Ivax Diagnostics ( IVD) fell 8.2% to $1.56, Oscient Pharmaceuticals ( OSCI) was down 6% to $1.25, Nyer Medical Group ( NYER) lost 9.7% to $2.80, Alpharma ( ALO) was down 6.6% to $21.65, and Rigel Pharmaceuticals ( RIGL) was losing 3.8% to $9.20.