Until recently, renal crisis was the most significant cause of morbidity and mortality in patients with scleroderma (SSc). Nowadays, following the introduction of angiotensin-converting enzyme inhibitors used in renovascular hypertension, pulmonary fibrosis and pulmonary hypertension have become the most common causes of death in SSc. Consequently, the early diagnosis and treatment of pulmonary fibrosis is essential to improve morbidity and mortality in SSc patients. The aim of this study was to investigate the effect of intravenous cyclophosphamide pulse therapy in patients with SSc and evidence of active alveolitis assessed on a high resolution computed tomographic (HRCT) scan, and to compare the effect of cyclophosphamide pulse therapy with oral therapy. Sixteen consecutive patients with SSc were allocated alternately to the two treatment groups. Eight patients were treated with monthly cyclophosphamide pulse therapy (750 mg/ m2) for 12 months; the other eight patients were treated with oral cyclophosphamide (2-2.5 mg/kg/day) for the same period. All patients received concurrently prednisone (10 mg/day). Pulmonary function tests and HRCT scans were performed before therapy and at 6 and 12 months. In the oral cyclophosphamide group, three patients with a grade I pattern showed regression of disease extent. In the other five patients (one with grade II and four with grade III) the pattern and extent of disease remained stable during the study. No statistical differences were found in forced expiratory volume in 1 s, forced vital capacity and total lung capacity during the study period. The diffusing capacity for carbon monoxide increased significantly between baseline and 12 months (p = 0.043). In the cyclophosphamide pulse therapy group, seven patients with a grade I pattern showed regression of disease extent at 6 months (p = 0.018) and 12 months (p = 0.012). One patient with grade III remained stable during the study. In both groups the regression of the extent of disease estimated on HRCT was due to a decrease in the ground glass appearance. The extent of the reticular appearance remained stable throughout the study. Our results indicate that cyclophosphamide pulse therapy is effective in suppressing active alveolitis (ground glass appearance). Although in this study it is not possible to compare pulse therapy with oral therapy because of the different pattern seen on HRCT between the two groups, it seems that oral therapy is also effective in suppressing active alveolitis. Neither regimen improved pulmonary involvement when the reticular appearance predominated over the ground glass appearance on HRCT. It is concluded that either pulse or oral cyclophosphamide therapy may improve the outcome of SSc patients.