Eighteen-day-old seedlings of five maize hybrids (A619xH60, B73xM017, B73xPA91, B73xVA17 and A632xH96) were grown hydroponically and compared for inherent differences in lipid concentration and composition. These seedlings were also evaluated for their ability to tolerate mild osmotic stresses (-0.4 and -0.6 MPa, polyethylene glycol-induced), osmotically induced changes in lipid composition, and differences in membrane stability as measured by electrolyte leakage. Inherent differences among the hybrids included reduced dry matter accumulation, and lower total lipid and free fatty acid concentration in the leaves and roots of B73xVA17 and A632xH96 compared to A619xH60, B73xMOl7, and B73xPA91. No differences were apparent in the frea, glycosidic or esterified steryl fractions among hybrids. Distributional patterns of fatty acid and sterol composition differed among tissues but were similar in all hybrids. Osmotic treatments of -0.4 and -0.6 MPa resulted in significant reductions in the dry weight of B73xVA17 and A632xH96. Total lipid concentration increased significantly in the roots of all hybrids while there was a general trend for moderate increases in stems and leaves. Few, mostly insignificant differences, were observed in the free fatty acid, free sterol, steryl glycoside and steryl ester fractions. However, the stigmasterol to sitosterol ratio increased in all three steryl fractions in the roots of B73xVA17 and A632xH96 as a result of the osmotic treatments. B73xVA17 and A632xH96 also exhibited the greatest electrolyte leakage when leaf discs were subjected to osmotic stress. B73xVA17 and A632xH96 appear to be less· tolerant to osmotic stress than the other hybrids. This may be due to their comparatively earlier developmental growth stage at the onset of osmotic stress. Modification of lipids in these sensitive hybrids may reflect an initial stabilization of cellular membranes which, in turn, may have some adaptive value in terms of drought tolerance. / M.S.