Semen samples from 179 infertility patients were analyzed for type and number of white blood cells (WBC) by a combination of immunologic techniques. Forty-one (23%) had more than 10(6) WBC/mL semen (leukocytospermia). Semen parameters in patients with less than 10(6) WBC/mL were similar to those of 15 fertile donors. In contrast, the leukocytospermic group had significant reductions in total sperm number, percent sperm motility, sperm velocity, motility index, and total number of motile sperm. Patients with high concentrations of monocytes/macrophages (greater than 5 X 10(5)/mL; n = 27) had significantly reduced ejaculate volume; patients with high numbers of T lymphocytes (greater than 10(5)/mL; n = 19) had a significant reduction in sperm velocity; and patients with high levels of granulocyte elastase in semen (greater than 1,000 ng/mL; n = 26) had significant reductions in ejaculate volume, total sperm number, and total motile sperm number. There was no correlation between the presence of antisperm antibodies and leukocytospermia. Our data suggest that leukocytospermia may occur frequently in male infertility patients and show that elevated levels of WBC in semen are associated with poor semen quality. This provides further rationale for white blood cell testing in semen of male infertility patients, since antibiotic or anti-inflammatory therapy may be helpful in appropriately selected cases.