The long-chain fatty acids synthesized from acetate by an enzyme system reconstructed fom soluble fractions of pigeon liver have been separated and identified by a variety of techniques. Free palmitic acid and progressively smaller amounts of free myristic, lauric and decanoic acids are principally formed in this system. Small quantities of esterified long-chain acids with the properties of palmityl CoA were also found. Short-chain fatty acids do not accumulate, but small amounts of the hydroxamates of short-chain acids can be formed if acetyl CoA is used as substrate in place of acetate. HMG has been identified in the incubation mixture. Net synthesis of fatty acids was demonstrated by direct weighing, titration and radioactivity measurements. The specific radioactivity of the carboxyl carbon of fatty acids synthesized from carboxyl-labeled acetate was 1.7 times that of the average carbon atom in the entire chain. This finding is in agreement with the concept of fatty acid synthesis via head-to-tail condensations of acetate units.