Shares of biotech

Tanox

(TNOX)

plunged more than 40% and trading was halted after it was learned of a regulatory delay in approval for one of its drugs.

Tanox was off $10.29, or 40.6%, to $15.07 when trading was stopped shortly before 11 a.m. EDT. The company's asthma drug Xolair, to be marketed with partners

Genentech

TheStreet Recommends

(DNA)

and

Novartis AG

, was the subject of a letter from the

Food and Drug Administration

requesting more information.

As a result of the request, Genentech and Novartis said the drug would likely not be resubmitted until 2002 or 2003. In recent trading, Genentech was off 12%.