Plasma concentrations and peripheral blood cells containing cytoplasmic cytokines were monitored during the post-transplant period in 10 patients who had received allogeneic bone marrow transplants (BMT) for the correction of inherited genetic disorders. The presence of CD14-positive cells containing cytoplasmic interleukin-1 alpha and beta in the peripheral blood was indicative of acute graft-versus-host disease (GVHD). Plasma concentrations of IL-1 alpha, IL-1 beta and TNF-alpha were significantly raised in the GVHD group when compared with the uneventful days. There was, however, poor temporal correlation between the plasma concentrations and clinical manifestations of acute GVHD. Cells containing cytoplasmic IL-6 were present in the peripheral blood when patients had clinically suspected and/or microbiologically confirmed infection. The results from this study demonstrate that analysis of peripheral blood cells for cytoplasmic IL-1 alpha and IL-1 beta are better markers of acute GVHD than is monitoring plasma concentrations of these cytokines.