Summary— Investigation of 311 azoospermic males has shown that the combination of estimation of testicular size and plasma FSH allows the spermatogenic funciton of th testes to be accurately assessed by non-invasive method.

Patients with small testes and grossly elevated levels of plasma FSH have absent, or grossly impaired spermatogenesis, and do not require surgical exploraion. They should be advised with regard to adoption or artificial inseminaition.

Patients with large testes (5 cm) or an FSH level which is not grossly elevated require operation and should undergo a surgical exploration and the possible corretion of an obstructive lesion. A testicular biopsy is essential if no obstructive lesion is found as the histology of these patients may show a spermatolgenic arrest.