Sixty azoospermic men were investigated by means of testicular biopsy and estimation of serum follicle stimulating hormone (FSH) levels. High FSH levels when associated with small testes indicated severe testicular damage. We suggest that these findings offer sufficient evidence to regard such patients as infertile and that further investigation is unnecessary. In men with normal FSH levels testicular biopsy is still necessary for accurate diagnosis; in practice this may often be done at the same time as epididymovasostomy.