Gamma-glutamyl transferase (GGT) of the human seminal plasma and reproductive tissues was purified and its properties were compared to those of the enzyme from kidney. A single band of GGT was obtained by polyacrylamide gel electrophoresis. Purification was 1080-fold for seminal plasma, 206-fold for prostate, 608-fold for testis and 382-fold for kidney. Similar Km value (0.87-1.06 mM) and optimum pH (8.2-8.5) were obtained for the enzymes of the four different sources. Their thermal stabilities were identical. However, inhibitions by Zn2+ and Cu2+ were different between kidney and reproductive system GGT. Molecular mass of the native enzyme was 78 kDa for seminal plasma, prostate and testis and 79 kDa and 105 kDa for kidney. The subunit molecular masses of the enzymes from seminal plasma, prostate and kidney consisted of three proteins, suggesting the precursor form, and the heavy and light subunits of the mature form.