E xpression of IL-1 alpha and beta genes was studied in human blood PMN with close monitoring of the effects of contaminating mononuclear leukocytes (MNL). We provide evidence that PMN both transcribe and translate IL-1 alpha and beta genes after stimulation with LPS or IL-1 alpha. A combination of mouse thymocyte comitogen proliferation assay, ELISA, and immunocytochemistry was required to establish that IL-1 alpha and beta synthesis observed in preparations of PMN could not be accounted for by the low level of contaminating MNL. Synthesis of IL-1 beta in PMN exceeded that of IL-1 alpha, but little or no IL-1 alpha was released by PMN. Although increases in IL-1 mRNA after stimulation of PMN and MNL with LPS were similar, PMN were less efficient than MNL in translating IL-1 mRNA. In contrast, PMN and MNL IL-1 alpha and beta mRNAs were translated with equal efficiency in rabbit reticulocyte lysates, suggesting that synthesis of IL-1 in PMN is subject to some form of translational control. We conclude that PMN stimulated with LPS efficiently transcribe but inefficiently translate IL-1 genes relative to MNL. IL-1 beta transcription and translation predominates over that of IL-1 alpha, and IL-1 beta is the predominant IL-1 protein released by PMN. IL-1 can induce its own synthesis in PMN.