Human testis preparations appear to carry out both the synthesis and turnover of prostaglandins. Prostaglandins and prostaglandin metabolites were extracted from whole tissue. Testis microsomes converted both endogenous and exogenous substrate to prostaglandins. Microsomal prostaglandin biosynthesis was inhibited by indomethacin. Prostaglandin E2-9-ketoreductase was present in both the cytosolic and microsomal fractions of human testis. Prostaglandin metabolism by human testis has not previously been reported.