Maillard reaction products (MRP) have been reported by several authors to inhibit lipid oxidation in model systems as well as in food products. The antioxidative compounds formed have so far not been identified, nor has the mechanism of their antioxidative effect been elucidated. In the course of trying to isolate antioxidative components formed by the Maillard reaction between histidine and glucose, it was found that part of the antioxidative effect was lost during the isolation processing. The stability of the antioxidants was therefore studied in more detail. The antioxidants were found to be unstable in solution when exposed to air. When they were stored in nitrogen atmosphere, no loss of antioxidative effect was noticed. The oxygen sensitivity was found to be pH dependent. Within the studied pH range 2-10, the stability of the antioxidants decreased with increasing pH. An oxygen electrode could be used to measure the consumption of oxygen by the MRP. In the dry state and in concentrated solutions at low temperatures, the MRP were found to be fairly stable. The significance of this instability in a food system and in laboratory work with the antioxidants is discussed. © 1983 American Chemical Society.