- To assess the potential of short-term systemic administration of FSH for improving sperm quality, including ultrastructure, in teratozoospermic patients having normal endocrine profiles. Semen parameters were assessed prospectively using light microscopy (LM), biochemical analysis, and quantitative ultramorphological analyses within 2 months before FSH administration and within 5 days after the end of treatment. Samples were collected from patients who were referred to the male fertility clinic at Bar-Ilan University. Thirty-one patients with teratozoospermia who exhibited normal hormonal profiles and who failed to fertilize their wives in at least two previous IVF attempts (n = 17) or who had wives with apparent normal fertility unable to conceive for > or = 5 years (n = 14) were classified as subfertile. One hundred one males with no previous history of infertility, whose wives conceived after < or = 12 months of pregnancy expectation, served as the control group. Treatment was 75 IU FSH administered daily for 30 days. Pretreatment and post-treatment sperm evaluation of basic and quantitative ultramorphological analyses parameters. The hypothesis was FSH treatment may improve spermatid morphogenesis by its multiple actions on the Sertoli-gamete cell compartment without interfering with the testicular hormonogenic function. A significant improvement in agenesis of the acrosome and in the amorphous heads was observed, reaching normal values after treatment with FSH. The axonema deteriorated. No significant changes were observed in basic semen analysis parameters. Because malformations of the fine structure of the sperm head subcellular organelles seem to be prerequisites for the success of FSH treatment, ultramorphological examination of the sperm may serve as an indication for the probability of success of this treatment.