Ochratoxin A (OA) is a mycotoxin which has been found to occur in foods of plant origin, in edible animal tissues, as well as in human blood sera and tissues. The ability of OA to move up the food chain is aided by its long half-life in certain edible animal species. In this report, an evaluation of the health risks to Canadians due to the presence of OA in food products is presented. The first part of the report deals with the physicochemical aspects, mycology, laboratory production, analytical methods, and natural occurrence in plant products, animal products, and human tissues. The stability of OA in foods and feeds, the effects of food processing, and the removal from foods and feeds by physiochemical means are also discussed. From these data, the worst case estimate for the daily exposure of Canadians to OA, from the consumption of pork-based food products and cereal foods, is approximately 5 ng OA/kg body wt (mean of eaters) for young children, the highest consumption group on a body weight basis. The second part of the report deals with the metabolic disposition as well as the available toxicity database for OA in laboratory animals, farm animals, and humans. The major target for OA toxicity in all mammalian species tested is the kidney, and endemic nephropathies affecting livestock as well as humans have been attributed to OA. OA is also teratogenic, and in the fetus the major target is the developing central nervous system. Recent studies have provided "clear evidence" of the carcinogenicity of OA in two rodent species. OA was found to be nonmutagenic in various microbial and mammalian gene mutation assays, but weak genotoxic activity to mammalian cells was noted. In addition, OA was found to suppress immune function. Based on the NTP carcinogenicity study with OA in rats, the estimated tolerable daily intake in humans ranges from 0.2 to 4.2 ng OA/kg body wt, depending on the method of extrapolation used. In view of the toxic properties of OA, it is recommended that exposure to OA be kept to a minimum. In Canada, further monitoring programs are required to better define the overall residue profile of OA in cereal grains, animal feeds, animal food products, and human blood. Such data are required to better assess dietary exposure and to ascertain the need for regulatory controls or other control mechanisms.