Sulphites are extensively used in the food and drinks industry. Their toxicity has been previously evaluated by addition to the diet or drinking water of laboratory animals. Because interactions between sulphites and food constituents occur, the present work was conducted to determine the subacute and subchronic toxicity of sulphite-bound compounds in a finished product: manufactured biscuits. The studies were performed on Sprague Dawley, rats for 28 and 85 days of dietary exposure. Diets were prepared from sulphited or untreated (controls) biscuits with the addition of sugar, protein, vitamins and minerals according to the nutritional requirements of the animals. Groups of 10 male and 10 female rats were administered diets containing sulphited biscuits at levels of 0, 10, 35 and 75%, corresponding to 10-15, 35-45, 150-170 and 310-340 mg SO2/kg diet. In both studies, no death or clinical abnormalities were reported. Growth rate, food consumption and food conversion efficiency were not affected by treatment. No dose-related changes were observed for haematology, clinical chemistry, ocular examination, renal-function, urinalysis, organ weights or gross and microscopic examinations. The liver concentrations of vitamins A, B1, C and E were not significantly changed except for an increase in vitamin E in high-dose males after 28 days' exposure. Based on these data, the no-observed-adverse-effect level (NOAEL) of sulphites in baked biscuits was judged to be 310 mg SO2/kg diet or 25 mg/kg body weight/day.