Male Sprague-Dawley rats were treated 10 times either with 2 or 10 mg/kg s.c. prednisolone acetate or with 300 or 1,000 mg/kg p.o. D-penicillamine or with 100 or 300 mg/kg p.o. aminoacetonitrile bisulfate. Samples of dorsal skin were tested either longitudinally or perpendicularly to the body axis. Relaxation and hysteresis experiments were performed at different degrees of elongation. Finally, ultimate values were measured. In all groups, ultimate strain was much higher perpendicularly than longitudinally to the body axis. A dose-dependent increase of all parameters indicating strength or elasticity was found after prednisolone acetate treatment, whereas the indicators of viscosity showed a decrease. D-Peni-cillamine treatment decreased all parameters of strength and elasticity and increased viscosity and plasticity. Aminoacetonitrile bisulfate induced biphasic changes: after high-dose treatments strength and elasticity were increased and viscosity decreased. The results are discussed in view of changes of biochemical composition and cross-linking of collagen.