To investigate the effect of leukocytospermia on standard semen analysis and sperm function tests such as acrosome reaction, hypoosmotic swelling, antisperm antibody binding and cervical mucus penetration, a prospective clinical study was performed. Two hundred and nineteen male infertility patients undergoing investigation and treatment were included in the study. There was a significant association between acrosome reaction positivity and leukocytospermia according to WHO (World Health Organization) criteria. Increased hypoosmotic swelling test score, higher sperm concentration and enhanced acrosome reaction were closely related to leukocytospermia. When the patients were divided into subgroups according to seminal leukocyte concentrations, acrosome reaction and hypoosmotic swelling were observed to be higher in semen samples with higher leukocyte concentrations compared to those with low seminal leukocyte concentration. In addition, higher sperm concentrations were observed in semen samples with increased leukocyte levels compared to semen samples with low leukocyte levels. These results suggest that leukocytospermia may have a favorable effect on some sperm functions at seminal leukocyte concentrations between 1 and 3x10(6)/ml.