AbstractPrevious workers have claimed that tempeh oil contains a potent fat antioxidant. These claims were based solely on measurements of peroxide value during accelerated storage of tempeh oil alone or as an additive to other unsaturated oils. Oxygen absorption rate measurements indicate that tempeh oil actually has weak prooxidant activity. Fermentation of soybeans to produce tempeh generates high levels of free fatty acids. FFA promote rapid decomposition of peroxides so that the levels in the oil never increase substantially during oxidation. Consequently, PV is a poor index of oxidation rate in oils which are high in FFA. Our experience with tempeh oil does not confirm earlier observations of its efficacy as an antioxidant.