Interstitial pulmonary fibrosis is the reason of death 40% patients with systemic sclerosis (Scl), proximately 10% patients with rheumatoid arthritis (RA), and 5-7% of those with dermatomyositis (DM) and overlaps syndromes. Etiopathogenesis of the disease is stil unknown, therefore the adequate treatment is difficult. The aims of the study were to evaluate how intravenous cyclophosphamide (CYC) infusions influence on pulmonary fibrosis activity and find out how safe is this form of drug administration during 12-month follow-up in rheumatic diseases patients. The study comprised 22 patients (19 F and 3 M) aged 45-71 years (mean 57.8). In 12 of them interstitial pulmonary fibrosis was observed in the course of systemic sclerosis, in 4 it was concomitant with RA, and in 4 with dermatomyositis and 2 patients with mixed connective tissue diseases (MCTD). Pulmonary fibrosis was diagnosed basing on their medical examination, X-ray chest, high resolution computed tomography (HRCT) of the lungs, spirometry. The patients were administered i.v. 1.0 g CYC: 6 infusions in one-month intervals in the introductory therapy; in the supportive therapy – 3 infusions every 2 months (9 infusions in all). Directly and 1-2 days before of each infusion blood count, ESR, CRP, transaminase activity and serum creatinine concentration were measured. Spirometry was done every 3 months, chest X-ray and HRCT every 6 months. After 6 month of the treatment the progression of lungs fibrosis on X-ray chest was no observed in all of patients and during next 6 month (12-month follow-up) there was no progression in 73% patients. Adequately in HRCT were 83% after 6 and 80% after 12 month for start treatment. There were no worsening of FVC in spirometry in 88% patients after 6 month therapy, and in 67% patients after one year follow-up. Serious adverse events were no observed.