Posttransplant lymphoproliferative disorders remain an uncommon complication of heart transplant with a high mortality rate reported after conventional therapies. Four patients with posttransplant lymphoproliferative disorders, of whom 3 were CD20 positive, received intravenous dosages of rituximab, 375 mg/m(2), weekly, for 6 ± 2 weeks. The overall response rate was 75% with 3 complete responses (CD20 positive) and 1 case of progressive disease (CD20 negative). Rituximab should be considered as a first-line therapy for patients with CD20 positive posttransplant lymphoproliferative disorders.