This study examines the concentrations of polycyclic aromatic hydrocarbons (PAHs) in cigarettes and sidestream cigarette smoke. All 16 gas-phase PAHs and fourteen particulate-phase PAHs were determined in sidestream cigarette smoke for four brands of cigarettes. The median total of gas-phase and particulate-phase PAH concentrations after two cigarettes were smoked were 79.6 ng/m 3 and 10.0 ng/m 3 , and the concentrations were several times higher than before smoking. Median PAH increases in the air samples were 1050 ng per cigarette for gas-phase PAHs and 228 ng per cigarette for particulate-phase PAHs. Gasparticle partition coefficients (Kp) of PAHs in air samples before and after smoking were correlated with the subcooled liquid vapor pressures (PLº) of PAHs. The slopes of log-log plots of Kp versus PLº before and after smoking were -0.270 and -0.575, respectively. PAH partitioning between the gas and particle phases after smoking was closer to equilibrium state because the slope was closer to -1. Furthermore, all 16 PAHs were determined in the cigarettes. The medians of total PAH concentrations in the four brands of cigarettes were 353 ng/g before smoking and 1130 ng/g after smoking. Median PAH increase in the cigarette samples during smoking was 1410 ng per cigarette. The relationships in the concentration of the between total suspended particulate (TSP) and total particulate-phase PAHs, and between total gas-phase PAHs and total particulatephase PAHs were significantly positive. These findings imply that lowering the amount of TSP generated will lower the amounts of PAHs generated.