The photochemically induced addition of bromotrichloromethane to a series of chlorine-substituted ethylenes has been studied in gas-phase experiments. Addition to a carbon atom of the olefin not carrying a chlorine atom leads to formation of a normal adduct. When the addition of trichloromethyl radicals or bromine atoms occurs at a carbon atom carrying a chlorine atom the major products are CCl2CXCX2 and BrCXCX2 respectively, where CXClCX2 represents the original chloro-ethylene. The rate of trichloromethyl radical addition to a chlorine-substituted site is slower than the rate of addition at CF2 and much slower than addition to CH2. Arrhenius parameters for the addition of CCl3· to the CH2 end of vinyl chloride have been measured: k(CH2)=(1·1 ± 0·4)× 107 exp(–3400 ± 200)/RT l mol–1 s–1R, the gas constant, is taken to be 1·987 cal mol–1 K–1 and subsequent energies are expressed in cal mol–1(1 cal = 4·19 J).