Platelet-activating factor(PAF) enhanced interleukin-1(IL-1) activity by the interaction with a specific receptor in rat alveolar macrophages. In this study, we investigated the role of endogenous arachidonate metabolites and intracellular calcium mobilization in the PAF-induced IL-1 activity. Alveolar macrophages were preincubated with 5-lipoxygenase and cyclooxygenase inhibitors 30 min before the addition of PAF and lipopolysaccharide(LPS). After 24h culture, IL-1 activity was measured in the supernate of sample using the thymocyte proliferation assay. Inhibition of 5-lipoxygenase by nordihydroguaiaretic acid and AA-861 completely blocked the PAF-induced enhancement of IL-1 activity with IC50 of 2 ㄍM and 5 ㄍM, respectively. In contrast, the inhibition of cyclooxygenase pathway by indomethacin and ibuprofen resulted in the potentiation in PAF-induced IL-1 activity with maximal effect at 1 ㄍM and 5 ㄍM, respectively. In addition, leukotriene B4 and prostaglandin E2 production were observed in PAF-stimulated alveolar macrophage culture. As could be expected, 5-lipoxygenase and cyclooxygenase inhibitors abolished PAF- stimulated leukotriene B4 and prostaglandin E2 production, respectively. The effects of PAF on intracellular calcium mobilization in alveolar macrophages were evaluated using the calcium-sensitive dye fura-2 at the single cell level. PAF at any dose between 10-16 and 10-8 M did not increase intracellular calcium. Furthermore, there was no effective change of intracellular calcium level when PAF was added to alveolar macrophages in the presence of LPS or LPS⁢LTB4, and 4, 24 and 48h after treatment of these stimulants. Together, the results indicate that IL-1 activity induced by PAF is differently regulated through subsequent induction of endogenous 5-lipoxygenase and cyclooxygenase pathways, but not dependent on calcium signalling pathway.