Abstract: A novel hazard index of mainstream cigarette smoke for risk evaluation of cigarette products was developed.163 commercial cigarettes,including international and Chinese brands,American blend and Virginia blend cigarettes,purchased in China were investigated.The yields of 29 toxic chemicals(4 TSNAs,3 PAHs,8 carbonyls,7 phenolic compounds,HCN,NO,NO_x,NH₃,CO,Nic and Tar) in mainstream cigarette smoke were determined,and the toxicity of cigarette smoke was measured employing a bacterial mutagenicity assay(Ames Salmonella mutagenicity assay) with cigarette smoke condensate(CSC),the MTT cytotoxicity assay with CSC,the micronucleus assay in vivo with CSC,and a mouse inhalation study.In order to establish the functional relationships between smoke yields and smoke toxicity,the correlation between the yields of 29 toxic chemicals and 4 toxicity assay results were investigated.The key toxic chemicals were screened with uninformative variable elimination(UVE) and genetic algorithm.The results indicate that the contributions of 7 toxic chemicals(CO,HCN,NNK,NH₃,BaP,phenol and crotonaldehyde) to the toxicity of mainstream cigarette smoke were significant.The correlation models between 7 key chemicals and 4 toxicity assay response were developed by multiple linear regression analysis.The R square for Ames assay,MTT assay,in vivo micronucleus assay,and mouse inhalation study were 0.504,0.595,0.571,and 0.524,respectively.The relative errors of leave-one-out cross-validation for all models were less than 40%.Based on the yields of 7 toxic chemicals in mainstream cigarette smoke,a novel hazard index was deve-loped to evaluate the risk of mainstream cigarette smoke;the calculation is as follows:H=Y_CO/C₁+Y_HCN/C₂+Y_NNK/C₃+Y_NH3/C₄+Y_BaP/C₅+Y_PHE/C₆+Y_CRO/C₇Where:Y——yields of toxic chemicals in mainstream smoke;C₁~C₇——Constant.Applying this index,the hazard of mainstream cigarette smoke of main cigarette products from the China market was evaluated.The results indicate that the product ranking according to the hazard index is different from the ranking according to tar deliveries,so the hazard index may be a more reasonable way to evaluate the risk of cigarette products.