We evaluated the cytolytic function, phenotypic characteristics, and cytokine levels of 22 patients with non-Hodgkin's lymphoma and 7 with Hodgkin's disease receiving interleukin-1 alpha (IL-1 alpha) following autologous bone marrow or peripheral blood stem cell transplantation. IL-1 alpha was given i.v. over 6 hr, between day 0 and day +13 posttransplant. On day +14, cells from patients receiving high-dose IL-1 alpha (3.0 micrograms/m2/day) had significantly enhanced killing of natural killer (NK)-sensitive and -resistant lymphoma targets compared to those treated with low-dose IL-1 alpha (0.1, 0.3, or 1.0 microgram/m2/day). The differences in cytolytic function between the two groups persisted but were not as striking on day +28. Patients receiving higher-dose IL-1 alpha had a significantly increased proportion of CD3+ T cells on days +14 and +28, while the proportion of CD16+ and CD56+ NK cells was decreased compared to those of patients treated with the lower dose. There were no detectable levels of IL-2, interferon-gamma, or tumor necrosis factor-alpha in the plasma of patients receiving IL-1 alpha posttransplant. However, higher-dose IL-1 alpha therapy was associated with significant increases in serum IL-6 levels in comparison to those in patients receiving low-dose IL-1 alpha. IL-1 alpha may increase cytolytic function post-bone marrow transplantation; it remains to be determined, however, whether this would have an impact on decreasing relapse rates of patients undergoing transplantation for lymphoma.