Alterations in the physical properties of dermal collagen by streptozotocin-induced diabetes mellitus were investigated in young adult Lewis rats by mounting standardized rings of tail skin on an Instron Universal Testing Apparatus and measuring the thermally induced isometric contraction and stress at rupture of the tissue. Diabetes significantly increased the maximum tension (Tmax) of the contraction and raised the temperature for the Tmax while the stress at rupture (TR) was unaffected when compared with values for controls fed ad libitum and controls fed restricted diets for weight loss equivalence. The diabetes-mediated changes in thermal contractility appeared to be independent of the collagen concentration or negative caloric balance and resembled the reported age-related change in rat skin collagen.