The influence of minor amounts of pro- and anti-oxidants on the kinetics of the autoxidation of fat has been evaluated. The reaction rates of oxygen with the substrates were found to follow the same basic equation, hitherto established for pure substrates. There is evidence that the surface of the reaction vessel also acts as a reaction catalyst and its effect is proportional to the area of glass in contact with lipids. Oxidation is enhanced by trace metal ions as well as by surface-active compounds (e.g. hydroperoxides and sterols). Antioxidants such as α-tocopherol and butylated hydroxyanisole inhibit the oxidation by delaying the start of oxygen consumption (the induction period) while retarders like amino acids only decrease the rate of oxidation. Thus pro- and anti- oxidants affect either the start or the rate of oxygen consumption. The empirical formula dx/dt = k [O2] (1-x/n) f′(t) was found applicable to the different stages of oxidation.