The lipid composition of the sperm membrane has been shown to exert a significant effect upon the functional quality of spermatozoa. We have studied fatty acid composition of the phospholipids in spermatozoa in asthenozoospermic and normozoospermic men and determined the ratio of polyunsaturated fatty acids (PUFAs) to saturated fatty acids of spermatozoa of these two groups. Fatty acid concentration of spermatozoa was determined in 15 asthenozoospermic and eight normozoospermic semen samples by thin layer chromatography and gas chromatography. The most abundant polyunsaturated and saturated fatty acids in normozoospermic samples were docosahexaenoic acid (DHA 22 : 6 omega3, 98.5 +/- 4.5 nmol per 10(8) spermatozoa, mean +/- SE) and palmitic acid (103 +/- 17 nmol per 10(8) spermatozoa) respectively. The mean +/- SE values of DHA and palmitic acid in asthenozoospermic samples were 53.9 +/- 11.6 and 145 +/- 14.7 nmol per 10(8) spermatozoa respectively. Compared with normozoospermic samples, asthenozoospermic samples showed lower levels of PUFA and higher amount of saturated fatty acids. The mean +/- SE ratios of sperm PUFA/saturated fatty acids in asthenozoospermic and normozoospermic samples were 0.66 +/- 0.06 and 1.45 +/- 0.16 (P < 0.001) respectively. This study demonstrates that spermatozoa of asthenozoospermic men have lower levels of PUFA compared with saturated fatty acids. This may be contributory to the poor motility noted in samples from these men.