Interleukin-1 (IL-1) is one of the principal cytokines that participate in local regulation of many reproductive functions. The present study was undertaken to determine whether mRNAs for IL-1α, IL-1β, and IL-1 type I receptor (IL-1R) are expressed in bovine corpora lutea (CL), and whether luteal cells respond to treatment with IL-1α and IL-1β during the luteal phase. Bovine CL were classified into five stages (early, Days 2–3; developing, Days 5–6; mid, Days 8–12; late, Days 15–17; and regressed, Days 19–21). IL-1α, IL-1β, and IL-1R mRNAs were detected by reverse transcription-polymerase chain reaction (PCR) in all luteal stages examined. Densitometric analysis of PCR products revealed increases of the mRNA of IL-1α and IL-1R in the CL of the regressed stage (P < 0.05). There was less mRNA for IL-1β in the regressed stage than in the developing and mid stages (P < 0.05). When developing, mid, and late luteal cells were treated with IL-1α (1–30 ng/ml) or IL-1β (1–30 ng/ml) for 24 h, IL-1α and IL-1β dose-dependently increased prostaglandin (PG) F_2α and PGE₂ production by the luteal cells of all stages (P < 0.05), indicating the presence of functional IL-1R in bovine CL. However, progesterone synthesis was not affected by either IL-1α or IL-1β treatment. Stimulation with IL-1α and IL-1β decreased the PGE₂:PGF_2α ratio in the developing stage (P < 0.05), whereas it increased the ratio in the mid stage (P < 0.05). In the late stage, the ratio of IL-1β-treated cells was greater than that of IL-1α-treated cells (P < 0.05). Overall results indicate that genes for IL-1α and IL-1β are expressed and a functional IL-1R is present in the bovine CL throughout the luteal phase, and suggest that IL-1α and IL-1β have different roles as local modulators to regulate PGF_2α and PGE₂ production during the luteal phase.