Production of 6-hydroxynicotinic acid, an important starting material for the synthesis of modern pesticides through bacterial position-specific hydroxylation of nicotinic acid, was investigated. Resting cells of Serratia marcescens IFO 12648 were found to catalyze the potential hydroxylation activity of nicotinic acid to produce 6-hydroxynicotinic acid. The optimum culture conditions of S. marcescens IFO 12648 for the accumulation of 6-hydroxynicotinic acid were investigated. The addition to the culture medium of molybdenum and iron ions and of nicotinic acid as an inducer greatly enhanced the hydroxylation activity. Under the optimum conditions, 98.5% of the added 2.2 M nicotinic acid was converted to 6-hydroxynicotinic acid, and the highest yield achieved was 301 g of 6-hydroxynicotinic acid per liter of reaction mixture containing 3.98 g dry weight of resting cells during a 72-h reaction at 35 degrees C.