Release of some cytosolic (aspartate aminotransferase, alanine aminotransferase and lactate dehydrogenase) and brush border (y-glutamyltransferase and alkaline phosphatase) enzymes from renal cortical slices was studied in vitro. Renal cortical slices were prepared freehand from 3-month-old male and female Wistar rats of different hormonal status. Some male and female rats were castrated at 1 month of age and a portion of castrated males and of naive males and females were S.C. treated with testosterone (10 mg kg-' body wt.) on alternate days for 3 weeks. Females had higher alanine aminotransferase (77.5 f 2.8 nmol 100 mg-' tissue), lactate dehydrogenase (5.01 2 0.24 Fmol) and alkaline phosphatase (1.63 f 0.15 mol) activities than male rats (20.4 f 0.9, 3.99 f 0.19 and 0.91 f 0.02, respectively). On the contrary, aspartate aminotransferase and y-glutamyltransferase were similar. Among cytosolic enzymes, alanine aminotransferase and lactate dehydrogenase appeared to be sexual hormone-dependent enzymes: castration significantly increased enzyme activities in males (49.6 f 1.1 for the former; 5.30 rf: 0.15 for the latter) and caused significant decreases in females (alanine aminotransferase only 47.1 f lS), whereas testosterone pretreatment decreased activities in cortical slices from female (48.1 * 3.6 and 3.81 f 0.07, respectively) and castrated male (27.4 rf: 1.8 and 4.05 rf: 0.15, respectively). Moreover, exogenous testosterone increased aspartate aminotransferase in males (1.05 f 0.01 pmol) and castration increased it in both sexes. The activity of brush border enzymes was increased by testosterone pretreatment and decreased by castration (mainly alkaline phosphatase).