Testicular biopsy specimens from 16 fertile and 10 subfertile men with normal male karyotype were studied quantitatively to provide histological and cytogenetic data for a basis of reference in assessing abnormalities of spermatogenesis. Histological studies included estimation of the proportion and activity of germinal epithelium and an assessment of tubular morphology. In cytogenetic preparations, counts were made of cells at different stages of meiosis. Studies of cells at diakinesis included chiasma counts and percentage of cells with dissociated sex chromosomes. One fertile and six subfertile men showed decreased germinal activity; the six subfertile men also had decreased MII/MI ratios. Other findings were similar in the two groups.