Na+- and K+-activated and Mg2+-dependent adenosine triphosphatase, Mg2+-activated adenosine triphosphatase and Ca2+- and Mg2+-activated adenosine triphosphatase activities were determined in washed spermatozoa and in two fractions (pellet and supernatant) of seminal plasma of oligoasthenospermic patients and men with normal spermiograms. The activities of triple adenosine triphosphatase oligoasthenospermics were significantly lower than those of normals. The morphologic features of spermatozoa of oligoasthenospermics were of normal standards. Possible explanations for the significantly lowered triple adenosine triphosphatase activities from patients with oligoasthenospermia are given with special reference to the ion transport functions of the triple adenosine triphosphatase enzyme system.