The pattern of fatty acids produced by the fatty acid synthetase complex of Brevibacterium ammoniagenes under several conditions was examined. The fatty acid synthetase obtained from B. ammoniagenes produced oleic acid as well as saturated fatty acids (palmitic and stearic acids). The relative proportions of palmitic to stearic acids varied over a wide range. Such alterations were dependent on the malonyl-CoA concentration and the ratio of acetyl-CoA to malonyl-CoA concentrations. At malonyl-CoA concentrations higher than 100 microM, stearic acid accounted for more than 90% of the saturated fatty acids and the pattern of fatty acid synthesized was independent on the ratio of acetyl-CoA to malonyl-CoA. At malonyl-CoA concentrations lower than 100 microM, raising the acetyl-CoA/malonyl-CoA ratio increased the percentage of palmitic acid. However, the proportion of oleic acid produced remained almost constant under all conditions tested.