Much controversy surrounds the clinical significance of an increased concentration of white blood cells (WBC) in the male ejaculate. The World Health Organization's classification of leukocytospermia is a concentration > 1 x 10(6) WBC/ml. The aim of this study was to assess the association of varying concentrations of leukocytes to sperm morphology evaluated by strict criteria. Semen samples were collected from a total of 79 patients. Round cells on the initial semen analysis were stained for identification of polymorphonuclear granulocytes (PMN) as the largest group (50-60%) of white blood cells using the Endtz Method commercially produced as Leucoscreen. Diff Quick Staining Kit was used for sperm morphology assessment and 200 spermatozoa were assessed per slide. Data were evaluated using two cut-off criteria, at 0.5 x 10(6) WBC/ml and 1 x 10(6) WBC/ml. Mann-Whitney U-values at both < and > 0.5 x 10(6)/ml PMN (P < 0.001) and at < and > 1.0 x 10(6)/ml PMN (P < 0.015) showed differences between percentage normal forms. Spearman's rank correlation coefficient for PMN concentration showed a negative correlation (P < 0.01) with percentage normal sperm morphology and positive correlation for midpiece abnormalities (P < 0.04). These data support the hypothesis that PMN have a role in the increase of abnormal spermatozoa, particularly those with midpiece abnormalities, by as yet unknown mechanisms.