Measurements were made of the rates of reduction of various oxidizing agents on passive zirconium in acid solutions of sodium sulfate at temperatures ranging from 25° to 85°C. The oxidizing agents included in these experiments were oxygen, hydrogen ion, and cupric ion and hydrogen peroxide in the presence of oxygen. The kinetic orders of reduction were determined from potentiostatic experiments in which the current was determined as a function of concentration. Unit and fractional orders were observed with oxygen reduction, and fractional orders from about 0.5 to 0.65 were observed for Cu++ and . Possible mechanisms are suggested in which charge transfer through the film is assumed to play a predominant role.