Ochratoxin A is a mycotoxin with pronounced nephrotoxic potency in all species of single-stomach animals studied; it is a major disease determinant of porcine nephropathy and a disease occurring endemically in several countries. This disease is comparable with Balkan (endemic) nephropathy, suggesting a common causal relationship. Ochratoxin A has been found in foodstuffs in many countries, but the highest frequency of ochratoxin A contamination in foods (10.3% of 1,553 samples of foodstuffs) was encountered in an area of Yugoslavia, where Balkan (endemic) nephropathy is prevalent. Detection of ochratoxin A in human blood samples confirmed the prevalent exposure to this food contaminant. Relative risk calculations indicated a tendency to an association between this mycotoxin and Balkan (endemic) nephropathy, supporting the hypothesis of a causal role of ochratoxin A in this disease.