The karyotype of 443 infertile males has been studied (infertility of unknown etiology). The sample has been divided in 3 groups according to the data of their spermogram: Gr 1--101 males with a normal spermogramm (selected through the sterility of their couple). Gr 2--185 infertile males with oligospermy (less than 20 millions spermatozoal/ml). Gr 3--157 infertile males with azoospermia. This study shows: --No significant difference in chromosomal aberration rate between group 1 and general male population. --A rate of 5% chromosomal aberration in group 2 (versus 0.7% in normal male population p less than or equal to 10(-8], nearly exclusively balanced translocations. --A rate of 21% chromosomal aberration in group 3, nearly exclusively 47, XXY or 46, XX (p less than or equal to -9). The karyotype is unlikely to bring any information in infertile males with normal spermogram; on the contrary it is of valuable interest in infertile males with abnormal sperm.