Male Sprague-Dawley rats were treated with D-penicillamine (D-pen) in doses of 100, 250 or 500 mg/kg per day for 10, 32, 42 or 70 days. In addition animals were examined 28 days after withdrawal from 42 day's treatment with D-pen at 100 or 500 mg/kg per day. Pair-fed rats served as controls. The changes in aortic collagen, glycosaminoglycans (GAGs), DNA and RNA were studied. D-Pen had a dose- and time-related solubilizing effect on aortic collagen, which regained normal resistance to extraction within 28 days after cessation of the treatment. In contrast, D-pen caused a progressive accumulation of hydroxyproline (Hyp) in the aortic wall during and after treatment, probably mediated by an increased number of matrix synthesizing cells, as judged by augmentation of the DNA content in the presence of unaltered Hyp/DNA and RNA/DNA ratios. The relative amount of type III collagen was increased after 500 mg/kg per day D-pen for 10 and 42 days. High doses of D-pen increased the percentage of water in the aortic wall and reduced the ratio of Hyp to total tissue protein, suggesting an increased content of water-binding substances. This was confirmed by GAG accumulation. Hyaluronic acid (HA) and chondroitin 4,6-sulphate (CHS) were predominant after 32 and 42 days, whereas CHS, heparan sulphate (HS) and dermatan sulphate (DS) prevailed after 70 days of treatment. These observations suggest that processes of repair and regeneration are elicited secondary to the inhibitory effect of D-pen on aortic collagen and elastin crosslinking. Hypertrophy of the vessel wall may imply an increased rigidity, resulting in further increase of the susceptibility to haemodynamic injury.