This preliminary study was designed to examine whether nitric oxide, a reactive nitrogen intermediate produced by leukocyte metabolism of L-arginine, could reduce sperm motility. Increasing doses (10(-6)-10(-4) M) of the nitric oxide-generating drug, sodium nitroprusside (SNP) were added to motile sperm preparations and incubated over 20 hr. Quantitative sperm motility measurements were made using a computer-assisted motility analyzer in each treated sample and controls over this time period. The percentage of motile sperm, progressive motility, and concentration of motile cells were all significantly reduced with all doses of SNP. This effect was not observed in preparations treated with oxyhaemoglobin (HbO2). Mean path velocity was unaltered. Sperm viability in SNP treated sperm did not differ significantly from that of control sperm over the same time period. We conclude that further experiments are required to determine whether the production of nitric oxide/reactive nitrogen intermediates in vivo by activated leukocytes could be a contributory factor in the development of immunologic infertility.