Intensive plasma exchange therapy with fresh-frozen plasma as the replacement fluid was used to manage ten patients, five with acute and five with chronic immune thrombocytopenic purpura (ITP). Therapy was started because of severe hemorrhage (1 case), failure to respond to steroid therapy (6 cases), or steroid dependence (3 cases). After a median of four exchanges over 6 days (median total volume removed, 11.7 liters), initial responses, defined as a platelet count greater than 100,000 per microliter at the end of the exchange series, were observed in 80 percent of the patients treated. Two adolescents, ages 16 and 17 years, with chronic ITP failed to respond to plasma exchange therapy and subsequently responded to splenectomy. Prolonged remissions of 9 months and greater than 2 years were observed in two patients with acute ITP; in patients with chronic ITP, no prolonged remissions occurred. Neither pre-exchange levels of platelet-associated immunoglobulin G (PAIgG) nor circulating immune complexes predicted the response to plasma exchange, although serially determined PAIgG levels correlated with the severity of ITP and response, or lack of response, to plasma exchange. We conclude that intensive plasma exchange merits further study in patients with acute ITP unresponsive to steroid therapy to determine if the need for splenectomy is reduced. In selected patients with chronic ITP, exchange therapy may provide short-term adjunctive benefit.