The toxicity of smoke from cigarettes containing tobacco, Cytrel tobacco supplement, or mixtures of the 2 materials, was investigated using 6 short term test methods. The tests used were rat trachea organ culture and mouse skin thickening tests, which may provide information on carcinogenicity, a ciliatoxicity test, an alveolar macrophage viability test, a haemolysis assay and a thiol inactivation test to provide measures of irritant and cytotoxic effects. In each case a response to the smoke from cigarettes containing tobacco alone was detected, while the magnitude of this response declined as the proportion of tobacco supplement in the blend increased. The least response was found with smoke from cigarettes containing Cytrel tobacco supplement alone.