Acute myeloblastic leukemia (AML) blasts have been shown to produce a variety of cytokines in culture such as interleukin-1 (IL-1), IL-6, granulocyte-, macrophage-, and granulocyte-macrophage colony-stimulating factor (GM-CSF), and tumor necrosis factor-alpha (TNF alpha). Using two sensitive and specific enzyme-linked immunosorbent assays for IL-1 beta and GM-CSF, we document in the present study that the production of the two cytokines by AML blasts in culture is coordinated. First, we observe a striking correlation between the levels of GM-CSF and IL-1 beta released by the cells. Thus, a high production of IL-1 beta is always concordant with a high production of GM-CSF and, conversely, low production of IL-1 beta is concordant with low levels of GM-CSF. Second, neutralization of intrinsic IL-1 using antibodies that are specific for IL-1 alpha and -1 beta suppresses the release of GM-CSF by the cells. Third, neutralization of the endogenous source of IL-1 also results in an abrogation of GM-CSF mRNA. Fourth, the production of both IL-1 beta and GM-CSF is up-regulated by exposing AML blasts to an exogenous source of IL-1, suggesting a positive regulation of autocrine growth factor production. Taken together, our results indicate that GM-CSF production by AML blasts is mediated by endogenously produced IL-1. Both IL-1 beta and -1 alpha are produced by AML blasts, although IL-1 beta appears to be more abundant. Spontaneous colony formation by AML blasts is abrogated by the addition of neutralizing antibodies against IL-1 beta and GM-CSF, whereas each antibody alone has little effect on blast proliferation. Taken together, our results are consistent with the view that the production of IL-1 beta by AML blasts supports autocrine growth in culture, through induction of CSFs or other cytokines that stimulate blast proliferation.