Both partners of 198 consecutive infertile couples were evaluated. Studies in the female included clinical evaluation of ovulation for a minimum of two menstrual cycles, investigation of tubal patency, and evaluation of sperm survival in cervical mucus. Six semen specimens were analyzed from each male. Laparoscopy, scrotal exploration, and testicular biopsies were performed as required. Where indicated, the female was treated intensively. The only therapy offered to the males was ligation of varicoceles, if present. The couples were grouped on the basis of sperm counts, total sperm counts, motile sperm counts, and total motile sperm counts, and the incidence of pregnancy was computed. Pregnancy rates of approximately 50% occurred in couples where sperm counts or total sperm counts were in the range of 5 to 60 million/ml or 25 to 200 million/ejaculate, respectively. When sperm counts were over 60 million/ml or total sperm counts over 200 million/ejaculate, pregnancy rates increased to above 70%. These observations emphasize the importance of considering infertility as a problem of a couple rather than as a specific disorder of one of the partners. These data also demonstrate a lack of direct correlation between sperm density in the ranges of 5 to 60 million/ml and pregnancy rates in couples where the wife is treated intensively.