The specific activities of the enzymes cinnamic acid 4-hydroxylase and cytidine-5'-diphospho-choline: 1,2-diacylglycerol cholinephosphotransferase (E.C. 2.7.8.2) were determined in microsomal fractions from a) dark-grown and b) irradiated parsley (Petroselinum hortense Hoffm.) cell suspension cultures. Cinnamic acid 4-hydroxylase activity was increased 4-fold after light treatment, while cholinephosphotransferase activity was decreased by about one third of its original activity. It can be concluded that increased microsomal lecithin biosynthesis is not required for the light-induced increase of cinnamic acid 4-hydroxylase activity, although the latter enzyme has previously been found to require a lipid cofactor for activity.