Interleukin-1 (IL-1) is a cytokine with a wide range of effects on a variety of cell types. By hybridization with human IL-1 alpha and IL-1 beta cDNA probes, the corresponding ovine cDNAs were isolated from a stimulated alveolar macrophage cDNA library. The sequences of these cDNAs showed that ovine IL-1 alpha and IL-1 beta encode proteins of 268 and 266 amino acids, respectively, with both the nucleotide and amino acid sequences showing a high degree of homology with their human, mouse and bovine equivalents. In a mammalian COS cell-expression system these cDNAs produced biologically active IL-1. Further experiments demonstrated the importance of sequences within the 3' untranslated portion of the cDNAs in determining the level of expression of these molecules. The analysis of expression of IL-1 alpha- and IL-1 beta-specific mRNA in response to endotoxin, phorbol myristic acid (PMA) or PMA plus ionomycin revealed a distinct pattern of differential regulation of the two genes. From genomic analysis both IL-1 alpha and IL-1 beta appear to exist as single copies in the ovine genome.