Shares in

Martek Bioscience

(MATK)

were hammered Friday after the Columbia, Md.-based company said European authorities had revoked a patent.

Martek shares fell $5.28, or 11.1%, to $42.30 in heavy trading. Almost 4 million shares changed hands, about six times the daily average.

The company said it intends to file an appeal that will automatically reinstate the patent so that it will remain in force during the appeal process.

Martek said the European Patent Office yesterday revoked its European DHA/ARA oil blends patent, as a result of what it called "challenges made by two potential competitors."

"Management believes that the outcome of this matter will not have a short- term impact on the Company's sales into the infant formula industry due to its other issued patents and the automatic reinstatement process," the company said. "However, it is possible that if the European DHA/ARA oil blends patent matter is not resolved favorably, in the long term the Company could experience increased competition that may result in decreased sales in Europe."

The company's leading products are nutritional oils used as ingredients in infant formula, foods and dietary supplements.