Chronic idiopathic thrombocytopenic purpura is an autoimmune disease characterized by antibody-mediated destruction of platelets. To maintain the platelets above the symptomatic level, we administered anti-D (100 micrograms for 5 consecutive days) in 19 children with idiopathic thrombocytopenic purpura (ITP). Four patients did not respond to treatment. Fifteen responded with an increase in the average platelet number to 76,000/microL on the 7th postinjection day. Within 45 days, however, platelets dropped to 27,000/microL. Three months after this study, two patients from the study group were re-administered anti-D in daily injections for 5 consecutive days, as was done previously. Monthly administration of anti-D in two patients maintained platelets above 30,000/microL for periods of five and six months. We concluded that monthly administration of anti-D after five consecutive daily injections can maintain platelet levels above the symptomatic level and may provide a corticosteroid-free safe interval of nearly five months.