Ultrastructural features of round-headed human spermatozoa.

Two cases of the round-headed spermatozoa syndrome are described, with the main emphasis on the ultrastructural features of the spermatozoa. Essentially, the first type (type I) of these cells has round heads, lacks an acrosome and its intrinsic enzymes, and lacks a postacrosomal sheath; patients with this condition are absolutely infertile. This is the classical Schirren-Holstein model for the round-headed spermatozoon. Other types of round-headed spermatozoa might exist (Type II), which may possess remnants of the acrosome and are capable of fertilisation.