Punch biopsies of skin were obtained from the forearms of 3 patients with progressive systemic sclerosis with diffuse scleroderma before and after treatment for 1 year or more with D-penicillamine. While on therapy, each patient studied had demonstrated a marked reduction in skin thickening. Collagenase-sensitive protein and glycosaminoglycan accumulation were measured in fibroblast cultures derived from these biopsies. No differences were observed pre- and post-treatment. We conclude that although D-penicillamine may exert its effect in vivo on connective tissue synthesis, maturation and/or turnover, fibroblasts remaining in the thinned dermis retain their potential for increased synthesis of connective tissue.