The widely assumed correspondence between fluorescence and photochemistry in photosynthetic systems has recently been challenged by observations on the triplet state of bacteriochlorophyll in reaction centres of Rhodopseudomonas spheroides. In order to check this assumption we have conducted a precise determination of the quantum efficiency of bacteriochlorophyll photooxidation in reaction centres at room temperature. We find a quantum efficiency of 1.02 +/- 0.04 in contrast to a value of about 0.7 predicted from the variations in fluorescence yield.