Time-resolved resonance absorption of OH was used to study the reactions of OH, generated by flash photolysis of mixts. contg. H2O or N2O + H2, with H2, D2, HCl, and DCl at 210-460 DegK. Second-order rate consts. were detd. and the obsd. kinetic isotope effects were compared with predictions of the transition states by using semiempirical potential functions to est. the transition state properties. Preliminary measurements on reaction of OH with HBr and HI gave crude values for the rate consts.