The flame chemistry of neutral tin has been examined quantitatively for the first time. In premixed H2+O2+N2 flames in the temperature-range 1800–2500 K, the predominant neutral species is confirmed to be SnO. Diffuse bands in the region 470–510 nm, previously attributed to SnO, arise from SnOH. Through a second-law procedure, a value of D°0(Sn—OH)⩽355±35 kJ mol–1 was determined. The likely mechanism of formation of electronically excited SnOH is discussed. Significant catalysis by the of H and OH radical recombination rates is described. A simple catalytic cycle involving gaseous SnO and excited SnOH is thought to be responsible for this effect.