Eighty-six patients with progressive systemic sclerosis were given coagulation factor XIII intravenously in different dosage regimens. The mean duration of treatment was 19 +/- 18 months and patients were followed up for 22.9 +/- 18.8 months. Improvement or stabilization of the lesions was obtained in 44/86 patients and exclusively concerned skin lesions; there was no improvement in visceral lesions. The drug was well tolerated in short-and long-term treatment. It is concluded that factor XIII demonstrated lasting effectiveness in one-half of the patients treated.