Acyl-CoA:O-lysophospholipid acyltransferase activity was measured in extracts of developing safflower (Carthamus tinctorius var. UC-1) seeds. Acyltransferase activity was present in all subcellular fractions. The microsomal acyltransferase activity was solubilized with either 30 mm-n-octylglucoside, 1% deoxycholate, or 100 μm lysophosphatidylcholine. The pH optimum of the lysophosphatidylcholine-dependent acyltransferase activity was at 9.0. Among the various acyl-CoA's tested, oleoyl-CoA was the best substrate and with it the enzyme had a Km of 9.5 μm. Among the various acyl acceptors tested, lysophosphatidylcholine (oleoyl) gave the highest activity and the optimal concentration was 30 μm. Acyltransferase activity was stimulated by ethanol and inhibited by bovine serum albumin and divalent cations.