Twenty patients with severe systemic disease were treated intermittently with bolus intravenous injections of cyclophosphamide in doses of 0.5 to 1 g. The diseases were systemic lupus erythematosus in 9 cases, systemic necrotizing angiitis in 5 cases, Behçet's disease in 4 cases, Horton's disease in 1 case and dermatomyositis in 1 case. The rationale for this treatment was resistance to previous therapies in 9 patients, initial severity of the disease in 8 and the need for prompt reduction of corticosteroid dosage owing to side-effects in 3 other patients. No death or haemorrhagic cystitis was observed over a cumulative 120 month-patients period. Bacterial infection occurred in 6 cases, including pneumonia (3), and 1 case each of staphylococcal septicaemia, purulent meningitis and urinary infection: none of these infections were life-threatening, and all were cured without sequelae. The drug was well tolerated biologically, except for a moderate fall in neutrophils, lymphocytes and platelets. The systemic disease was stabilized or improved in 16 patients. It remained active and required corticosteroids at the same dosage level in 4 cases. It is concluded that bolus injections of cyclophosphamide are well tolerated in short-term treatments but that their effectiveness must be confirmed by controlled studies.