Lenses were cultured in Medium 199 containing 14C acetate for 3, 6, 12 and 20 hours. There was a linear increase in incorporation into the total lipids with time. The total lipid extract was subjected to two-dimensional chromatography and incorporation into the individual classes of lipids was measured. For all time periods approximately 70% of all incorporated radioactivity was seen in the sterol and phosphatidyl choline (PC) fractions. Incorporation was observed in phosphatidyl ethanolamine (PE), aldehydes of PC and PE plasmalogens, phosphatidyl inositol (PI), PC plasmalogens, PE plasmalogens, sphingomyelin (SM), phosphatidic acid (PA) and phosphatidyl serine (PS). The fatty acids of the total lipids were methylated and subjected to gas chromatography, and individual fatty acids were collected. The greatest incorporation occurred in palmitic acid (16:0) and myristic acid (14:0) with minor amounts in lauric acid (12:0). These are the major products of de novo synthesis. The remainder of the radioactivity appeared in fatty acids 18 carbons or longer, which are the products of an elongation mechanism.