The laser flash photolysis of I was studied over a wide pressure range in several bath gases. At low pressures the obsd. quantum yield for photolysis at 6943 .ANG. is independent of the gas d., whereas at higher pressures the quantum yield decreases with increasing gas d. This phenomenon is discussed in terms of the cage effect, and the measured yields are compared with model calcns. The expts. also provide information on the second order rate consts. for I atom combination.