Sperm cell membranes are susceptible to peroxidative damage through an excess of reactive oxygen species. The objective of this study was to determine seminal plasma glutathione peroxidase (GPX) and superoxide dismutase (SOD) activity and relate these to phospholipid profiles and phospholipid-esterified fatty acid composition of spermatozoa. Seminal plasma GPX and SOD activity, phospholipid, phospholipid-esterified fatty acid composition and malondialdehyde (MDA) of spermatozoa were assayed in 10 normozoospermic and 25 asthenozoospermic subjects. Mean seminal GPX and SOD activity in normozoospermic men were not significantly different from asthenozoospermic men. A significant positive correlation was observed between seminal plasma GPX activity and phosphatidylcholine content (r = +0.77, P = 0.037) and there was a significant negative correlation with lysophosphatidylcholine content (r = -0.89, P = 0.02) in normozoospermic sperm samples. Positive correlations were found between SOD activity and polyunsaturated fatty acid composition of spermatozoa. MDA content in the spermatozoa of asthenozoospermic subjects was significantly higher than in normozoospermic males (P < 0.05). Negative correlations were found between MDA content and seminal SOD activity and arachidonic acid content of spermatozoa from normozoospermic samples (r = -0.5; P = 0.046, r = -0.9; P = 0.001 respectively). Seminal plasma GPX and SOD provide protection against lipid peroxidation of phospholipid and phospholipid-bound fatty acids in normozoospermic samples.