The deuterium isotope effect for the vinyl radical combination and disproportionation reactions have been investigated. Protonated or deuterated vinyl and methyl radicals are produced from the 193 nm photolysis of protonated or perdeuterated methyl vinyl ketone. On the basis of product yield measurements, no isotope effect for the combination reactions of either vinyl-vinyl or vinyl-methyl has been observed. From the relative yields of ethylene, an isotope effect of k(H)/k(D) = 1.20 is determined for the vinyl-vinyl disproportionation reaction.