The activities of 5 enzymes in urine and renal tubules were measured after administration to male Wistar rats of small doses of ochratoxin A (145 micrograms/kg per day for 8-12 weeks, corresponding to 2 ppm in the feed) by intubation. These doses are in the range of natural contaminations found in food and feed. The enzymes examined were gamma-glutamyl transferase (gamma-GT), alkaline phosphatase (ALP), leucine aminopeptidase (LAP), lactate dehydrogenase (LDH), and N-acetyl-beta-D-glucosaminidase (NAG). The doses employed caused increased enzymuria and lower activities of tubular enzymes after 1 week of feeding. This suggests tubular injury. The change of the enzyme activities in the urine and in the tubules appeared in a cyclic way (degeneration and regeneration). Phenylalanine (20 ppm) partially prevented this action of ochratoxin A. The p-[14C]aminohippurate accumulation was inhibited by 60% in the second week but returned to almost normal level 6 weeks after the beginning of the treatment, suggesting an adaptation of the organism or a substitution of damaged cells.