Nine pigs were fed crystalline ochratoxin A [produced by Aspergillus ochraceus] in amounts corresponding to a feed level of 1 mg/kg for 3 mo. The only observable lesion that developed was kidney damage, identical to the naturally occurring porcine nephropathy. The changes of renal function were characterized by impairment of proximal tubular function, indicated by a decrease of the ratio TmPAH/CIn [maximal tubular excretion of p-aminophippuricacid/inulin clearance], of the ability to concentrate urine and by an increased urinary excretion of glucose. The decrease of the ratio TmPAH/CIn is correlated with time of exposure to ochratoxin A. The changes of renal structure were characterized by degeneration of the proximal tubules, leading to tubular atrophy accompanied by interstitial fibrosis. At the end of the experiment the kidney, liver, adipose and muscular tissue of the slaughtered pigs contained sizable amounts of ochratoxin A residues. As the pigs would have passed the meat inspection this represents a possible [human] health problem. The changes observed in this study were identical to those observed by feeding to pigs grains naturally contaminated with ochratoxin A.