The setting behavior of disulfide-enriched wool and disulfide-crosslinked silk obtained by treatment with a disulfide-containing crosslinking agent, bis $(eta-isocyanatoethyl)$ dissulfide was compared with that of untreated wool and silk under the absence and the presence of a reducing agent. Rearrangment of secondary bonds facilitated by cleavage of crosslinks as well as rearrangement of crosslinks itself seems to play an important role in the set stability.