Previous work suggested that interleukin (IL)-2 can be used for eradicating residual disease in autologous grafts and for preventing recurrence. We report a phase II study of autologous peripheral blood stem cell transplantation with in vitro IL-2 incubation of peripheral blood stem cells and posttransplantation IL-2 in patients with recurrent or refractory non-Hodgkin lymphoma. Salvage chemotherapy consisted of ifosfamide and etoposide. Responding patients underwent autologous peripheral blood stem cell transplantation. IL-2incubated stem cells were infused on day 0. IL-2 1 mIU/m 2 was given from day 1 until day 28. Four monthly maintenance cycles of IL-2 4 mIU/m 2 subcutaneously twice daily days 1 to 5 and days 8 to 11 were administered thereafter. Eighty-four evaluable patients were enrolled, and 60 proceeded to transplantation, of which 56 received IL-2-incubated stem cells. The average received dose of posttransplantation IL-2 was 30% to 50% of planned. Only 42 patients received maintenance IL-2. The average received maintenance dose of IL-2 was also approximately 30% of planned. Most dose reductions were due to toxicity or patient refusal. Three-year survival and progression-free survival for all registered patients were 43% (95% confidence interval [CI], 33%-53%) and 31% (95% CI, 21%-41%), respectively. For the 60 patients undergoing transplantation, they were 59% (95% CI, 46%-72%) and 44% (95% CI, 31%-57%), respectively. There was no relation between the dose of IL-2 received and outcome. Survival and disease-free survival of the study group were similar to those of a previous study cohort that received unmanipulated stem cells and no systemic IL-2. Administration of IL-2-incubated peripheral blood stem cells and intensive posttransplantation IL-2 was associated with considerable but rapidly reversible toxicity. No effect on long-term outcome was observed.