The rates of reaction, Arrhenius preexponential factors, and activation energies of CH2FCH2F (HFC-152) and CH3CHF2, (HFC-152a) for the abstraction reaction with hydroxyl radical were measured by a relative rate method. Temperature ranges were 287-409 and 286-403 K, respectively. Reference compounds for both reactants were ethane (k = 1.00 x 10(-11) e(-) (1094/T) cm(3) molec.(-1) s(-1)) and cyclopropane (k = 7.28 x 10(-11) e- (1356/T) cm(3) molec.(-1) s(-1)). Also, the JPL 97-4 recommendation for HFC-152a (k = 2.4 x 10(-12) e(-1260/T) cm(3) molec.(-1) s(-1)) was used as a reference for HFC-152 vs 152a experiments. For HFC-152, the combined results yielded an Arrhenius expression of k = 3.55 x 10(-11) e(-1014/T) cm(3) Molec(-1) s(-1). The result for HFC-152a was k = 1.86 x 10(-12) e(-1183/T) cm(3) molec(-1) s(-1). For both reactants, uncertainties in k(298 K) and E/R are believed to be less than 10% and 100 K, respectively. The experimental results are compared with predicted values based on previously observed group effects as well as the dependence of preexponential factors on the magnitude of the rate constant. The results are also compared to previously published values for these same compounds obtained by absolute methods.