Pentosan-protein material from rye is subject to oxidative gelation, Thus, solutions of a fraction (obtained by precipitating water solubles from rye with ethanol) gel when solutions of hydrogen peroxide and horseradish peroxidase are added. The gelation reaction is inhibited by ferulic and vanillic acid but not by fumaric acid. This suggests that the mechanism whereby gelation occurs is comparable to that of wheat pentosan-protein material, in that the ferulic acid aromatic ring and not the propenoic moiety is involved in the gelation. Enzyme treatments showed that although protein probably is not necessary for the oxidative process, the presence of the pentosan moiety is required. Cysteine residues in the protein most likely are not involved in the gelation because N-ethylmaleimide has no effect on gelation, and the inhibition of the gelation reaction by cysteine can be rationalized as an effect of competition for the hydrogen peroxide. Ascorbic acid also inhibited the gelation, and its role probably can be ascribed at least partially to the same mechanism. High concentrations of cysteine or ascorbic acid in the presence of peroxidase and hydrogen peroxide reduced the relative viscosity of a pentosanprotein solution to experimental readings below those of the ungelled control solution.