Groups of 48 male and 48 female rats were fed quillaia extract in the diet at levels of 0 (control), 0·3, 1·0 and 3·0% for 2 yr. The material had no adverse effects on death rate, water consumption, serum chemistry or haematological parameters or on the incidence of histopathological findings, including tumours. In the males given the 3% dietary level, the death rate, total leucocyte count at wk 108, incidence of kidney lesions and weights of the kidneys, heart and thyroid were all below the control values. These differences were explicable, however, in terms of a lowered body weight consequent on a decreased food intake. It is concluded that, in rats, quillaia extract fed at levels up to 3·0% in the diet did not have any carcinogenic effect. The no-untoward-effect level established in this study was 3·0% in the diet, approximately equivalent to an intake of 1·5 g/kg/day.