Through the use of available experimental data and thermochemical cycles, improved values for the enthalpy of formation and dissociation energy of the hydroxyl radical have been found. The results of the analysis give DeltaH degrees (0,f)[OH(X(2)Pi (3/2))] = 37.14 +/- 0.12 kJ/mol, D-0[OH(X(2)Pi (3/2))] = 35 584 +/- 10 cm(-1), and D-0[OH(A(2)Sigma (+))] = 19 011 +/- 10 cm(-1). These results are consistent with those found from H2O photoionization experiments but have a factor of 3 smaller uncertainty than the best results from the photoionization studies. The results disagree with the presently accepted values for these quantities, obtained from an analysis of spectroscopic data on the hydroxyl radical. Based on the new value for the enthalpy of formation of hydroxyl radical and additional experimental data, values for the enthalpy of formation have been found for ClOH (DeltaH degrees (0,f), = -73.99 +/- 0.12 kJ/mol) and BrOH (DeltaH degrees (0,f) = -47.7 +/- 1.8 kJ/mol).