To assess whether oligospermia in infertile men might be associated with abnormalities of another rapidly dividing cell population, namely, blood cells, we studied retrospectively hematologic indexes in 72 unselected men initially attending an infertility clinic and 119 healthy controls. Red cell and platelet parameters were similar in the two groups. The infertility clinic patients had significantly reduced total leukocyte counts (5818 +/- 179 versus 6397 +/- 174 per mm3; p less than 0.05). This leukopenia reflected a reduction in lymphocyte count (1697 +/- 69 versus 2206 +/- 80 per mm3; p less than 0.0001) but not in neutrophil count (3331 +/- 144 versus 3678 +/- 139 per mm3; p = NS). Lymphopenia was not correlated with sperm density. A prospective study of 24 fertile controls and 12 infertile, oligospermic men revealed no differences between these groups in numbers of lymphocytes, T lymphocytes, T4 (helper) lymphocytes, or T8 (suppressor) lymphocytes. In conclusion, lymphopenia noted retrospectively in men attending an infertile clinic was unrelated to sperm density and was not confirmed in a prospective study. Combined with normal red cell and platelet parameters these findings suggest that hematologic indexes are probably normal in infertile men.