Photocalorimetry was used to determine the current efficiency of the photoanodic oxidation of halide ions (0.2 M Cl-, Br- and I-) competing with that of water at a polycrystalline TiO2 (rutile) thin film electrode for a range of pH values. For Cl- and Br- the results were checked by chemical analysis (spectrophotometry, polarography) of oxidation products present in the electrolyte solution. Photocurrent efficiencies determined photocalorimetrically and analytically for the formation of halogens (Cl-2 and Br-2 + Br-3(-)) in acid solution were in satisfactory agreement. Observations made at pH 9 suggest the formation of ClO- and BrO- on the time scale of the experiments. The photocurrent efficiency for oxidation of the halide ions at a given pH was found to increase in the order Cl-, Br-, I- and to decrease, for each species, with increasing pH. This corroborates the trends reported by other workers from rotating ring disk electrode studies using rutile single-crystal electrodes.