Cigarettes impregnated with various preparations of Delta(9)-tetrahydro-cannabinol (Delta(9)-THC) and cannabidiol were artificially smoked, and the smoke was analyzed by means of gas chromatography and a combination of gas chromatography and mass spectrometry. Retention of the two test substances in smoke was 21 to 23 percent of the starting amount. The ratio of Delta(9)-THC to cannabidiol in smoke is different from that in starting material. It is suggested that these differences are the result of partial cyclization of the cannabidiol to Delta(9)-THC. An increase in the percentage of cannabinol in smoke is the result of a partial dehydrogenation drogenation of Delta(9)-THC or cannabidiol. No evidence for the isomerization of Delta(9)-THC to Delta(8)-THC or for the formation of new pyrolyzed products was found.