Following a 7-day control period, 5 male volunteers consumed, on each of 23 consecutive days, a weight of xanthan gum equal to 15 times the current acceptable daily intake (10 mg/kg b.w.) approved by the EEC and by the Joint FAO/WHO Expert Committee on Food Additives; thus, the lightest and heaviest of the volunteers consumed 10.4 g and 12.9 g respectively of xanthan daily. Measurements before and at the end of the test period showed that the ingestion of xanthan, as a pre-hydrated gel, acted as a bulking agent in terms of its effects on faecal wet and dry weight and intestinal transit time but had no significant effect on plasma biochemistry, haematological indices, urinalysis parameters, glucose tolerance and insulin tests, serum immunoglobulins, triglycerides, phospholipids and HDL cholesterol, breath hydrogen and breath methane concentrations. There was a moderate (10%) reduction in serum cholesterol and a significant increase in faecal bile acid concentrations. The data indicate that the ingestion of xanthan caused no adverse dietary nor physiological effects in any of the subjects. In particular, all of the enzymatic and other parameters that act as sensitive indicators of adverse toxicological effects remained unchanged.