We describe the preparation of monoclonal antibodies (Mabs) directed against recombinant bovine interleukin-1 beta (rBoIL-1 beta). These anti-IL-1 beta Mabs were designated SA10, SA12, SA13, SA15, and SA22, and were characterized on the basis of their epitope specificity and cross-reactivity with homologous and heterologous cytokines in enzyme-linked immunosorbent assays and immunoblot analyses. Additionally, the ability of these Mabs to neutralize IL-1 beta was tested in thymocyte costimulation assays. The ELISA titers of all Mabs ranged from 9.4 x 10(6) to 1 x 10(7). Data indicate that Mabs SA10, SA12, SA15, and SA22 neutralized both bovine macrophage-derived IL-1 (1:4) and rBoIL-1 beta (1 ng ml-1). All the Mabs against rBoIL-1 beta (SA10, SA12, SA13, SA15, SA22) were specific and did not cross-react with other cytokines tested, except recombinant human IL-1 beta (rHuIL-1 beta). This finding suggests that these Mabs recognize epitopes common to human and bovine IL-1 molecules. Competition experiments suggested that Mab SA22 recognized a different epitope and Mabs SA10, SA12, SA13, and SA15 recognized the same epitope on the rBoIL-1 beta molecule. These observations suggest that these Mabs could be useful reagents for developing immunoassays to measure bovine IL-1 beta from biological fluids and to study the immunoregulatory role of IL-1 in the bovine immune system.