Tridecanoic acid is a 13-carbon saturated fatty acid found in dairy products and also as a product of anaerobic biodegradation of n-hexadecane. It has been identified as a substrate of phospholipase A2. Saturated fatty acids with carbon chain lengths of C12 to C14 activated the alpha-, beta-, gamma-, and epsilon-subspecies of the protein kinase C, and this activation was synergistic with that by diacylglycerol. Tridecanoic acid(C13) was most effective among the saturated fatty acids examined.