Parenteral or dietary lipids have been shown to alter the acyl composition of tissue lipids effectively. It has been suggested that the changes in the acyl composition would modulate physiological responses by altering the kinetic properties and/or activity of the cellular enzymes. One such enzyme is protein kinase C whose activity is regulated by receptor-mediated phospholipid hydrolysis. In this study, we have examined the effect of cis- unsaturated fatty acid on the activity of protein kinase C and protein phosphorylation in the hippocampus. Our results suggest that cis-fatty acid indeed modulates protein phosphorylation in the hippocampus and the cis- fatty acid-induced protein phosphorylation can be attributed to the activation of protein kinase C.