Johnson & Johnson ( JNJ) shares fell early Friday after the company late Thursday said it had voluntarily withdrawn 300 of its Cypher stents for quality-control reasons. The New Jersey-based health care giant said the coating on six of the devices did not meet its specifications and has notified federal regulators. J&J rival Boston Scientific ( BSX) last summer had to recall a much larger number of its Taxus stents because of manufacturing problems, a move that pounded the company's stock. J&J and Boston Scientific are the only two companies with approval to sell drug-coated stents in the U.S. J&J was first to the market, but Boston Scientific has assumed market leadership. J&J recently announced plans to acquire Guidant ( GDT), another medical-device maker. Shares were down $1.09, or 1.7%, to $62.23 in the premarket.