Blast cells derived from peripheral blood of patients with acute myelogenous leukaemia (AML) were cultured in vitro and interleukin 1 receptor antagonist (IL1RA) concentrations determined in culture supernatants. AML blasts derived from patients classified as AML‐M4 and AML‐M5 subtype showed an increased release of IL1RA. IL1α and IL1β caused a similar increase in AML blast release of IL1RA, and addition of anti‐ILl antibodies decreased IL1RA release. IL1RA release from AML blasts was also increased by stem cell factor, tumour necrosis factor α (TNFα), granulocyte‐macrophage colony‐stimulating factor and macrophage colony‐stimulating factor, whereas interleukin 3, interleukin 6, leukaemia inhibitory factor and granulocyte colony‐ stimulating factor did not significantly alter IL1RA release. When investigating IL1RA serum levels, serum concentrations were decreased in acute leukaemia patients with chemotherapy‐induced cytopenia compared with healthy controls. Serum levels of both IL1RA as well as IL1β and soluble TNFα receptors increased when the leucopenic patients developed complicating bacterial infections.