The chemorheology of two cross-linked polyurethane elastomers containing (1) disulfide groups and (2) tetrasulfide groups was investigated by stress relaxation experiments. It was found that the tetrasulfide-containing elastomer underwent stress decay at a rate 10 times faster than the disulfide-containing elastomer, showing that the tetrasulfide linkage undergoes bond interchange much more rapidly than the disulfide linkage. Spectroscopic evidence is cited tending to confirm the greater stability of the disulfide linkage. The behavior of a cross-linked polyurethane elastomer without polysulfide linkages is presented for comparison.