Sennosides were tested in a wide range of toxicity studies to evaluate risk assessment. From acute studies, sennosides could be classified as only slightly toxic in rats and mice after a single oral dose. The LD5o values were about 5,000 mg/kg in both species. The cause of death was probably due to an extensive loss of water and electrolytes following massive diarrhoea. In subacute studies with rats (max. 20 mg/kg) and dogs (max. 500 mg/kg), sennosides caused no specific local or systemic toxicity. Minor increase in kidney weight in rats was toxicologically not relevant. In a 6-month study with rats, sennosides were tolerated without specific toxic effects in doses up to 100 mg/kg. Effects on food consumption, body weight gain and some biochemical parameters as well as slight renal lesions can be interpreted as secondary effects following chronic diarrhoea. Mutagenicity tests and reproduction toxicity studies showed no abnormal results.