Cigarette mainstream smoke from blended cigarettes with and without the addition of ingredients was assayed for its cytotoxicity and genotoxicity. In total, 333 ingredients commonly used in cigarette manufacturing were assigned to three different groups. Each group of ingredients was added at a low and a high level to the test cigarettes. The mutagenicity of the particulate phase of the resulting cigarette smoke was assayed in the Salmonella plate incorporation (Ames) assay with tester strains TA98, TA100, TA102, TA1535 and TA1537. The cytotoxicity of the gas/vapor phase and the particulate phase was determined in the neutral red uptake assay with mouse embryo BALB/c 3T3 cells. Within the sensitivity and specificity of the test systems, the in vitro mutagenicity and cytotoxicity of the cigarette smoke were not increased by the addition of the ingredients.