The spermiograms of an infertile man were unique in showing normal parameters except for the presence of total immotility in 100 per cent of the spermatozoa. In 100 per cent of the axonemes of such spermatozoa there was a consistent lack of arms on the doublets of the axoneme. The same feature was found in all stages of spermatid formation. Other less consistent abnormalities were the occasional appearance of extra coarse fibers and axonemal microtubules, and an abnormal relationship between the longitudinal columns of the fibrous sheath and the doublets of the axoneme. All other ultrastructural details compared well with normal spermatozoa.