AbstractThe characteristics of the enzyme γ‐glutamyltranspeptidase were determined in frog liver and compared to those of the rat. InRana pipiens, tissue distribution studies indicated the order of activity to be: kidney>>>liver>>nerve>egg>lung>heart>skeletal muscle in homogenates. In theRana pipiensrelative to the Fischer 344 rat, the activity of the liver enzyme was somewhat greater (1·8‐fold) and the kidney enzyme substantially less (25‐fold). Frog liver γ‐glutamyltranspeptidase displayed strain‐dependent differences in activity withRana pipiensandRana sylvaticaexhibiting comparable activities andXenopus laevisexhibiting 20‐fold lower activities. No influence of sex was apparent inRana pipiensin contrast to the sex dependent differences observed in the Fischer 344 rat: ♀ : ♂ = 7:1. In homogenates and plasma membrane fractions ofRana pipiens, Xenopus laevisand the Fischer 344 rat, high, and comparable relative specific activities, were observed, 8–11, coupled with protein yields of 2·2–2·5 per cent indicating the enzyme to be plasma membrane bound and associated with the sinusoidal surface of the liver cell. Both the frogRana pipiensandXenopus laevisand Fischer 344 rat liver plasma membrane enzymes displayed comparable temperature‐induced activation (1·51–1·74‐fold) but with a peak for the frogs at 60°C and for the rat at 50°C. Both Acivicin and maleate inhibited the liver plasma membrane γ‐glutamyltranspeptidase of bothRana pipiensand the Fischer 344 rat, but the frog enzyme was less sensitive (89 per cent decrease versus 97 per cent decrease) to 150 μM Acivicin and more sensitive (65 per cent decrease versus 35 per cent decrease at 150 mM maleate) to maleate. Kinetic studies indicated that the liver plasma membrane enzyme fromRana pipienshad aKmof 0·61 mM andVmaxof 55·6 nmol mg−1min−1and that from the Fischer 344 rat had