Pharmacological treatment of diffuse systemic sclerosis (SSc) directed at the tissue fibrosis has generally been ineffective. Many immunosuppressive drugs have been tried as therapy for SSc, regardless of the disease subtype and/or stage. The aim of this study was to show the efficacy and the toxicity of oral cyclophosphamide and prednisolone therapy on the prevention of fibrosis-based tissue damage in the early stages of the diffuse SSc. Twenty-seven patients with early diffuse SSc were treated with oral cyclophosphamide (1-2 mg/kg/day) plus oral prednisolone (40 mg/every other day) between the years 1995 and 1998. The results regarding the efficacy and toxicity of cyclophosphamide were compared with those of 22 early SSc patients who had been treated with oral D-penicillamine between 1992 and 1995. All the patients were evaluated using clinical and laboratory parameters every 6 months for 2 years. There was a significant improvement on the skin score, maximal oral opening, flexion index, predicted forced vital capacity (FVC) and carbon monoxide diffusing capacity (DLCO) in the cyclophosphamide group. The decrease in skin score in the cyclophosphamide group started earlier than in the D-penicillamine group. No life-threatening or irreversible adverse reaction was observed. This open study supports the use of oral cyclophosphamide plus prednisolone therapy to prevent fibrosis and its complications in the early stages of diffuse SSc.