Aristolochic acids (AA) have been considered as toxicants of plants which were found in plants of the family Aristolochiaceae. The most abundant acids in mentioned plants are aristolochic acid I (AAI) and aristolochic acid II (AAII). AA have been considered as causes kidney disease called Aristolochic acid nephropathy (AAN). AAN was initially discovered in patients of one Belgian clinic in Brussels specialized on treatment of patients leading to a decrease in their body weight. The first name of this disease was Chinese herb nephropathy (CHN). Later, it was discovered that one component of herbal preparation was changed by a mistake with the Aristolochiaceae plant. The second type of renal disease caused by AA was discovered in populations of countries along the Danube river, called as Balkan endemic nephropathy (BEN), which was probably caused by the contamination of grains with plants containing AA. These renal diseases (AAN and BEN) are often associated with development of upper urothelial cancer (UUC). AA (AAI + AAII) in organisms are subject to biotransformation leading to its reductive activation or oxidative detoxification. Both cytosolic enzymes [NAD(P)H:quinone oxidoreductase] and microsomal enzymes [cytochromes P450, NADPH:cytochrome P450 reductase] participate in their reduction. The...