Stimulation of protein kinase C (PKC) activity in lipid vesicles in vitro was achieved by pure molecular species of diacylglycerol (DAG), specifically 1-stearoyl-2-acyl-sn-glycerol substituted with 2-arachidonoyl,2-eicosapentaenoyl or 2-docosahexaenoyl (SAG, SEG, and SDG, respectively). PKC activity was measured in lipid vesicles containing 30 mol% 1-palmitoyl-2-oleoyl-sn-glycerol-3-phospho-L-serine (POPS), 68-70 mol% 1-palmitoyl-2-oleoyl-sn-glycerol-3-phosphocholine (POPC), and 0-2 mol% DAG in the presence of 20 microM calcium. Our results demonstrate that amplification of PKC activity differs significantly among these molecular species of DAG. In particular, SDG at 0.5 mol% is more potent in increasing PKC activity than is dioleoylglycerol (DOG), SEG, or SAG, and SAG and SDG at 1.0 and 2.0 mol% have similar potencies which are greater than those of DOG or SEG. These findings demonstrate that sn-2 substitutions in DAG by specific n-3 and n-6 polyunsaturated fatty acids increase the potency of DAG to stimulate PKC activity in vitro.