The IL-1-dependent proliferation of RPMI 1788, a human EBV-transformed cell line, was used to develop a biological assay system for IL-1. Preparations of rhIL-1 alpha and rhIL-1 beta, as well as rmIL-1 beta exhibited a specific biological activity (50% of the maximal response) between 5.8 x 10(8) and 8.6 x 10(8) U/mg. Remarkably, a 3-5-fold reduced specific biological activity was noticed for rm-IL-1 alpha, viz. 1.7 x 10(8) U/mg. The IL-1-dependent proliferation of RPMI 1788 cells was compared with other IL-1 test systems, such as the IL-1-mediated induction of IL-2 in EL4-NOB-1, LBRM-33-1A5 and thymocytes, and the IL-1-driven induction of cytotoxic activity by PC60 cells, the so-called CIA assay. The cytokine-dependent growth of RPMI 1788 cells is highly specific for IL-1, and no other cytokine tested induced a proliferative response. The presence of high concentrations of rmTNF, rhTNF or rhIL-6 did not interfere with the quantification of IL-1. Additionally, we evaluated the detection of IL-1 in the presence of mitogens, phorbol ester or calcium ionophore, as well as the determination of IL-1 in serum and PF samples of human and murine origin.