A statistical analysis was performed on infertile male patients who visited our urological clinic between Jan. 1976 and Dec. 1981. The incidence of infertile male was 9.9% of the total male out-patients. Age distribution of most of the patients ranged from 25 to 34 years old. Infertile period was most commonly within 5 years after they had married. In semen analysis, the cases of azoospermia and oligozoospermia (less than 50 x 10(6)/ml) accounted for 80% of all the infertile males. Testicular histology showed hypospermatogenesis or "Sertoli cell only" in most patients (more than 84.2%) who received testicular biopsy. Decrease in testicular volume was accompanied by an increase in the serum levels of luteinizing hormone and follicle stimulating hormone, but there was no relationship between testicular volume and testosterone. Most of the patients with a testicular volume of less than 12 ml were azoospermic. This suggests that there may be a suppression of spermatogenesis in small testes.