Extracellular Ca2+ stimulated fatty acid synthesis in isolated rat hepatocytes. Orthovanadate (0.2-2.0 mM), an inhibitor of Ca2+-dependent ATPases, stimulated fatty acid synthesis in both the presence and the absence of extracellular Ca2+. Insulin stimulated fatty acid synthesis only in the presence of extracellular Ca2+. The contribution of extracellular Ca2+ to insulin stimulation of fatty acid synthesis is discussed.