Groups of 45 male and 45 female inbred Wistar rats were given diets containing stevioside (85% pure) at 0, 0.2, 0.6 or 1.2% for 2 yr. After 6, 12 and 24 months, five rats from each group were killed for haematological and clinical biochemical tests. Growth, food utilization and consumption, general appearance and mortality were similar in treated and control groups. The mean lifespan of rats given stevioside was not significantly different from that of the controls. No treatment-related changes were observed in haematological, urinary or clinical biochemical values at any stage of the study. The incidence and severity of non-neoplastic and neoplastic changes were unrelated to the level of stevioside in the diet. The maximum no-observed-effect level of stevioside was 1.2%, and an acceptable daily intake of stevioside for humans of 7.938 mg/kg body weight/day is suggested.