Enzyme activities have been measured in needle biopsies from kidneys of pigs fed 1 ppm or 0.2 ppm of ochratoxin A for 1-5 wks. After feeding 1 ppm toxin for 1 wk, the activity of cytosolic phosphoenolpyruvate carboxykinase (PEPCK) was decreased by 40% and remained inhibited until the termination of the experiment (5 wk). The activity of gamma-glutamyl transpeptidase, a brush-border enzyme found in the proximal tubules, was reduced to a similar degree and remained inhibited. The activities of hexokinase, a cytosolic enzyme of general distribution in the nephron, and phosphate-dependent.