It is well-known that ethanol alters fatty acid and glycerolipid metabolism in liver, but most of the studies have been developed on rats, so little is known about the corresponding effects on human liver. We have chosen the Hep G2 human hepatoma cell line, which appears to be an excellent in vitro model system. Cells were incubated in ethanol containing medium (0-400 mM) for 48 h. Incorporation and metabolism of radioactive substrates (14C(U) glycerol,[1-14C] palmitic acid and [1-14C] eicosatrienoic acid (n-6) were analyzed in cellular and conditioned medium lipids. Cellular growth rate and lipid composition of control and ethanol-treated cells were also studied. The results showed that ethanol inhibited logarithmic cellular growth rate in a concentration dependent manner, without affecting viability. Ethanol (400 mM) did not modify cellular major lipid composition except for an increase of cholesteryl esters, but produced a decrease in the proportions of myristic, palmitic and palmitoleic acids. Ethanol enhanced the incorporation of radioactive fatty acids into cellular glycerolipids but did not alter the rate of incorporation of 14C(U) glycerol. This was attributed to an isotopic solution of the radioactive glycerol as a result of increased alpha-glycerophosphate biosynthesis. Incorporation of radioactive fatty acids and glycerol into conditioned medium glycerolipids were increased in cells incubated in presence of ethanol. The increased incorporation of 14C glycerol into conditioned medium together with a simultaneous diminution in labeling cellular glycerides suggest that there would be a stimulation of the export of these lipid classes to conditioned medium. Conversion of [1-14C] palmitic to oleic acid and eicosatrienoic to arachidonic acid were inhibited in 400 mM ethanol treated cells suggesting an inhibition of delta 9 and delta 5 desaturase activity.