Rate consts. for the reaction OH + OH + M -> H2O2 + M (M = N2, H2O) were detd. by using flash photolysis of H2O vapor in combination with quant. OH resonance spectrometry. For M = N2 expts. were performed at 253, 298, and 353 K and pressures of 26-1100 mbar. Under these conditions, the reaction is primarily in the low-pressure limit. Both the abs. value of k1,N20 and its temp. variation agree with theor. predictions and extrapolations from high-temp. dissocn. data. A pressure falloff of k1,N2 was obsd. On the basis of a theor. anal. of the falloff behavior, a high-pressure limiting rate coeff. is predicted.