We gave interleukin-6 (IL-6) to eight patients with AML in first relapse after a median remission of 20.5 weeks and one patient with AML refractory to initial induction therapy. All nine patients had 5-29% blasts in the marrow together with < 5000 circulating blasts/microliter (smoldering disease) with a median platelet count of 19,000/microliters at a median of 7 weeks after initiation of last chemotherapy. The dose was 3.75 micrograms/kg by subcutaneous injection daily for 14 days. None of the nine responded, with response defined as at least a doubling in platelet count to > 30,000/microliters provided neither the marrow nor circulating blast count doubled to > 30% or > 10,000/microliters respectively. Given these data, the likelihood of a 15% response rate in patients whose disease is in smoldering relapse after a short first CR is only 27%, with 15% being the expected average CR rate following chemotherapy in these patients. Rises in platelet count unrelated to spontaneous recovery after prior chemotherapy were seen in three patients and a rise in marrow blast percent in four. Our results suggest that IL-6 might be used in stimulating platelet recovery in AML patients who remain thrombopenic without evidence of leukemia after chemotherapy, unlike our patients whose marrow had 5-29% blasts prior to starting IL-6.