We compared DNA flow cytometry to morphologic evaluation of routine testicular biopsies as methods of monitoring spermatogenesis. The study group consisted of 14 azoospermic men and 5 others who underwent testicular surgery unassociated with fertility problems. The findings for both studies were divided into three groups: normal, moderately abnormal, and markedly abnormal. Correlations between the findings from routine biopsy and flow cytometry were good. Of 9 patients having normal testicular morphology, 7 had normal ploidy classes by DNA flow cytometry while 2 had moderately abnormal histograms. Of 5 cases with moderately abnormal morphology, 1 had normal, 1 had moderately abnormal, and 3 had markedly abnormal ploidy distributions. In 5 cases described as Sertoli cell only, all DNA histograms were markedly abnormal, consisting almost exclusively of diploid cells. DNA flow cytometry of testicular biopsies and aspirates has been demonstrated to be a rapid, reproducible, and objective approach in evaluating the infertile male and is a promising method to investigate spermatogenesis in an outpatient clinic in lieu of formal testis biopsy.