Laboratory studies of the 248 nm photooxidation of Fe(II) to Fe(III) in concentrated sulfuric acid solutions indicate that photochemical reactions in the sulfuric acid clouds of Venus are capable of affecting the composition of the atmosphere at high altitudes, by removing O2 and CO and regenerating CO2. Major primary processes are the production of SO3- radical ions by photolysis of solvated SO2, and of SO4- radical ions by photolysis of complex ions containing Fe(III), if traces of iron salts are present. Secondary processes are similar to those which result in the formation of acid rain in Earth's troposphere. ¿ 2000 American Geophysical Union