Ten patients with severe progressive systemic sclerosis were treated with cyclosporin A at dosages of 1.5-7.5 mg/kg per day:two patients showed a marked improvement with softening of the involved skin; in one patient there was healing of persistent digital ulcers; one patient showed initial improvement followed by a marked exacerbation; one patient was slightly improved; two patients were unchanged. The clinical results correlated well with levels of serum aminoterminal propeptide of type III procollagen. In the eight patients completing treatment, side-effects such as slight tremor and a transient increase in the serum creatinine and blood pressure were either absent or reverted to normal when the dosage was decreased, except one case who had to be treated with anti-hypertensive drugs.