Among those factors known to influence spermatogenesis, chromosomal aberration is perhaps the best known. A review of the literature on mitotic studies in infertile men showed that 12% of the azoospermic and severe oligozoospermic (sperm count less than 10 x 10(6)/ml) males had a karyotypic abnormality; they mainly consisted of an XXY constitution or a Robertsonian or reciprocal translocation. A similar review on meiotic studies revealed that 8% of the infertile males had some kind of cytogenetic error. Therefore, mitotic and meiotic studies are indicated in males with severe gamete impairment when the other possible causes have been eliminated.