In vitro toxicity assays have been used successfully to measure the effect of cigarette design technologies upon cigarette smoke toxicity. Incorporation of a low nitrogen blend and enhanced carbon filtration reduces selected vapor phase constituents leading to lessened sister chromatid exchange rates and cytotoxicity of the aerosol. Removal of tobacco leaf protein prior to pyrolysis results in cigarette smoke condensates (CSCs) with greatly reduced Ames Salmonella mutagenicity as measured in bacterial strain TA98. Pyrolysis temperature has also been shown to profoundly affect TA98 activities with significant amelioration occurring at aerosol formation temperatures less than 400 degrees C. Chemically simplified aerosol and particulate matter resulting from primarily heating rather than burning tobacco reduce Ames activity, chromosome damage and neutral red cytotoxicity. Traditional ventilation technologies also affect in vitro toxicity, as CSCs from highly ventilated cigarettes have been shown to be more mutagenic in the Ames test on a per milligram 'tar' basis than CSCs from higher Federal Trade Commission (FTC) 'tar' cigarettes. On the other hand, modification of flue-curing processes leading to significant reductions in leaf and smoke levels of tobacco-specific nitrosamines has not resulted in reductions in the in vitro toxicity of the smoke. Blending can also affect in vitro results as the smoke chemistries of flue-cured, burley and Oriental tobaccos result in different toxicities in in vitro assays. For example, the increase in nitrogenous compounds seen in burley CSCs as compared with flue-cured CSCs can lead to increased Ames mutagenicity. In vitro toxicology test batteries represent a sensitive technology for determining changes in the biological activity of whole smoke and smoke components following product design modifications.