The expression of adhesion molecules on human ejaculated spermatozoa was investigated by means of flow cytophotometry using monoclonal antibodies against eight different adhesion molecules. Spermatozoa from infertility patients who exhibited normal semen parameters showed specific fluorescence after incubation with antibodies against very late antigens VLA alpha 4, VLA alpha 5, VLA alpha 6, and corresponding matrix proteins laminin and fibronectin. Semen samples from men with teratozoospermia or oligoasthenoteratozoospermia were characterized by reduced expression of adhesion molecules. Normal and pathological semen samples differed mostly in the expression of VLA alpha 5. After artificial induction of the acrosome reaction by a cold shock method and incubation with 2 mM Ca2+, a changed pattern of adhesion molecules on the sperm surface was found for VLA alpha 6 as the most prominent molecule. After treatment of spermatozoa with 0.1% Triton X-100, the number of cells with adhesion molecules increased significantly. This result suggests that adhesion molecules are an integral part of sperm structure.