Recent studies have revealed a high prevalence of leukocytospermia (> 1 x 10(6) white blood cells ml-1 semen) in male infertility patients in the USA and certain European countries, and have implicated white blood cells as a cause of infertility. Since leukocytospermia may often be attributed to male genital-tract infections, its prevalence could vary widely in different populations depending on factors such as sexual practices and the prevalence of sexually transmitted pathogens. In the study described here the incidence of leukocytospermia was determined in a group of 101 male infertility patients and a small reference group of normal fertile men in Beijing, China. Seminal white blood cells (WBC) and WBC sub-populations were enumerated by peroxidase staining and immunohistological assay. Eight out of 101 (7.9%) samples from infertility patients and 0/10 samples from fertile donors were leukocytospermic. The incidence of leukocytospermia in the Chinese infertility patients was considerably lower than the 23% incidence observed in a recent study of infertility patients in the USA using a similar technique. All but one of the patients with leukocytospermia had a poor sperm count and/or poor sperm motility. However, due to the low incidence of leukocytospermia and the small number of patients in this group, a statistically significant association between leukocytospermia and poor semen quality was not attained. The simple peroxidase test correlated well with the more expensive and technically demanding immunohistological assay for detection of white blood cells in semen.