Haematopoietic stem cell transplantation (HSCT) has been proposed for refractory autoimmune diseases, including systemic sclerosis (SSc). A sequential Bayesian phase I-II clinical trial was conducted in SSc patients to assess the feasibility, the tolerance and the efficacy of autologous HSCT. Peripheral blood stem cells (PBSC) were collected using cyclophosphamide (4 g/m2) and recombinant human granulocyte colony-stimulating factor (5 micro g/kg/d) and reinfused after positive CD34+ selection. Conditioning used cyclophosphamide (200 mg/kg) or melphalan (140 mg/m2) according to cardiac function. The main end-point was the failure of the procedure, defined by failure of either PBSC mobilization, CD34+ selection or intensification procedure, or by procedure-related death. Among the 12 enrolled patients, three failures occurred: one PBSC mobilization, one CD34+ selection and one CD34+ intensification. Probability of graft failure was estimated at 0.286 (95% confidence interval: 0.095-0.54). Autologous PBSC (n = 10) or bone marrow (n = 1) transplantation was actually performed in 11 patients with one procedure-related death. Median time to neutrophil (> 0.5 x 10(9)/l) and platelet (> 25 x 10(9)/l) haematopoietic reconstitution was 12 and 10 d respectively. After 18 months (range 1-26), eight out of 11 patients have shown major or partial response. Non-myeloablative conditioning, followed by a T cell-depleted autologous PBSC or bone marrow transplantation, appears feasible with low toxicity in severe SSc with short-term clinical benefits.