The present study evaluates the changes in sperm motility due to H202 induced membrane damage. Washed human sperm suspended in HAM's F-10 (20-30 x 10 6/ml) were incubated (37 degrees Celsius) with varying concentrations (0-0.05%) of H202 for up to 15 minutes. Sperm were analyzed for % motility, % viability, the ratio of cholesterol to phospholipids (C/PL), and the degree of lipid peroxidation (LPO). Motility was monitored manually and viability was evaluated by the Eosin Y staining method. Total lipids were extracted with chloroform:methanol (1:2) and used in colorimetric determination of cholesterol and phospholipid contents (mcmol/106 sperm). Lipid peroxidation was measured by the production of malondialdehyde (nmol MDA/108 sperm). The results (mean +or- SEM, n=8) indicate a dose a time-dependent effect on % motility during the 15 minute incubation period. In comparison to control (8 +or- 4%), samples incubated with 0.01% H202 exhibited a 25 +or- 3% decrease in % motility, while a complete loss of motility was observed with 0.05% H202. No significant differences in decrease in sperm viability were observed between control (211 +or- 4) and H202 (0.01%) treated samples (14 +or- 2%). An increase of (54 +or- 5%) in lipid peroxidation was observed with 0.01% H202, as compared with an 18 +or- 1% increase in control samples at 15 minutes. The C/PL ratio increased by 46 +or- 4% at 15 minutes in H202 treated samples while showing a 34.3% decrease in control samples. H202 inhibited sperm motility while increasing membrane LPO and C/PL, without altering sperm viability. It would appear that lipid peroxidation and alteration of sperm membrane composition lead to the loss of sperm motility.