The photolysis of formaldehyde was studied at 313, 334, and 366 nm in the range 80–120° and 9–40 Torr, over a 300-fold range of incident intensity. Some heterogeneous thermal decomposition was noted at these temperatures. It was found that [Formula: see text] and ΦCO were independent of intensity at low intensities which suggests that CHO → CO + H was unimportant in our system. From the zero-intensity extrapolations of Φ it was possible to obtain [Formula: see text] for CH2O + hv → H + CHO and [Formula: see text] for CH2O + hv → H2 + CO. [Formula: see text] and [Formula: see text] were found to vary considerably with wavelength and the values obtained are compared with literature data.