Phenylethanol is an important tobacco flavor commonly used in many commercial cigarette brands. 14C-Phenylethanol was used in this study to determine its mainstream and sidestream transfer efficiencies and to identify major decomposition products. When radiolabelled cigarettes were smoked in a total recovery apparatus, 13, 21.6, and 40.7% of the recovered activity was found in the mainstream TPM (MSTPM), the filter, and the sidestream TPM (SSTPM), respectively. Mainstream and sidestream gases accounted for 0.4 and 20.4% of the activity, respectively. The various smoke fractions were separated by TLC and quantified with a Berthold TLC scanner. An ammonia fixation technique was used to resolve phenylethanol from its major decomposition products. Only 6% of the MSTPM activity was intact phenylethanol. Thus, the transfer efficiency of phenylethanol to MSTPM is only 0.7%. Most of the radioactivity in MSTPM was found to be benzoic acid and phenylacetic acid. Of the radioactivity retained by the filter, 89% was intact phenylethanol, indicating that phenylethanol is selectively removed by cellulose acetate filters. The removal efficiency for phenylethanol is about 96% while that for the two acids, PAA and BA, is 22% and 11%. Of the SSTPM radioactivity, 52% was intact phenylethanol. Thus, the transfer efficiency of phenylethanol to SSTPM is about 19.9%.