hIL-1αa and hIL-1β were demonstrated and measured in culture supernatants of peripheral blood monocytes and mononuclear cells by sensitive and specific enzyme immunoassays. Two components for both hIL-1α and hIL-1β were demonstrated by gel filtration of culture supernatants: one with the same molecular weight as recombinant hIL-1α or hIL-1β and the other with a molecular weight of about 30,000. The production of hIL-1α and hIL-1β increased 1.6 to 38-fold in the presence ofEscherichia coli (E. coli)lipopolysaccharide. Levels of hIL-1α and hIL-1β became almost plateau within 24 h in culture supernatants of monocytes but became maximal within 12–18 h and decreased afterwards in culture supernatants of mononuclear cells, suggesting that hIL-1α and hIL-1β were produced by monocytes and consumed or degraded by other cells. In addition, hIL-1α and hIL-1β were detected in sera from patients with various disorders but not in sera from healthy subjects.