Myotonic muscular dystrophy (MMD) is a genetic disease caused by a defective enzyme, myotoninkinase. Male patients with MMD are reported to have reduced fertility. The purpose of this work was to study sperm capacitation and acrosome reaction in the ejaculates of sterile males with MMD and of healthy males (control group). The expression of the specific D-mannose receptors was explored by microscopic examination and by flow cytometry analysis. In addition, the binding patterns of Pisum sativum (PSA) lectin to acrosome content and outer acrosomal membrane in the spermatozoa of each group were analysed. Both the capacitation and the acrosome reaction in the spermatozoa of the MMD group were deficient and these findings strongly suggest that these anomalies may account for the sterility of these patients.