Lipids synthesized from acetate-1-14C in vitroin human dermis, epidermis, and sebaceous glands were examined. On the average, epidermis incorporates more 14C into lipids than dermis does in a given specimen. On per milligram basis, epidermis is several times more active than dermis.The lipids were separated into eight classes by chromatography on Unisil and Florisil columns. 14C was found in all lipid classes. The major amounts of 14C were found in the sterols, glycerides, and polar lipids of both dermis and epidermis, but greater proportions of 14C were found in the sterol and polar lipid fractions of epidermis than in corresponding fractions of dermis. Synthesis of squalene and triglycerides appeared to characterize the activity of the sebaceous glands.The epidermis excised from suction blisters was found active in synthesizing lipids from acetate-l-14C, and the activity appeared to increase after the ingestion of 100 g of glucose, indicating metabolic regulation of lipid synthesis in the epidermis.