The mass balance for chlorine and bromine in the burning 1R1 Kentucky reference cigarette has been determined using neutron activation analyses. Gas radiochromatography has been used to measure dynamically the amounts of gamma-emitting isotopes as they elute from a gas chromatograph. The sidestream and mainstream gas phases which elute from a gas chromatograph appear to be qualitatively identical in their organohalogens, differing only in their quantitative values. The results show that a substantial conversion of ionic halides to organohalogens takes place during smoke formation and this transformation has a threshold temperature below that established during either the puffing or static burn modes of the cigarette. The chemical nature of the halogens present in the mainstream particulate smoke was 10.8% organochlorine, 88.6% ionic chloride, 13.3% organobromine and 86.0% ionic bromide.