Ozone was photolyzed at 248 nm in 40 Torr nitrogen with small amounts of water or hydrogen added in a cooled or heated flow cell, to measure the O + OH rate constant at 136-377 K. Rate constant values were determined by kinetic modeling of the OH decays in excess O as monitored by laser-induced fluorescence and are in reasonable agreement with current recommendations. Results may be summarized by the expression k = 11.2 x 10(-11) T-.32 e(177/T) cm(3)/molecule/s.