We have investigated the regulation of transforming growth factor β1 gene expression in a variety of porcine immune cell populations, including peripheral blood mononuclear cells (PBMC), peripheral blood monocytes, alveolar macrophages and lymphoid cells from various swine lymphoid tissues. Using porcine transforming growth factor β1 cDNA probes in Northern blot assays, messages of 2.5 and 3.5kb TGFβ1 mRNA were detected in the cells investigated. A variety of mitogenic and immunomodulatory substances were examined for their ability to induce TGFβ1 mRNA expression. These include phorbol 12-myristate 13-acetate (PMA), phytohemagglutinin (PHA), concanavalin A (Con A), lipopolysaccharide (LPS), dexamethasone (Dex), tumor necrosis factor (TNF) and interleukin (IL)-1α. While low level constitutive expression of TGFβ1 mRNA was detected from all cells investigated, PMA treatment of PBMC and alveolar macrophages resulted in a more than 10-fold increase in the steady-state level of TGFβ1 mRNA within 2 hr of PMA addition. Also, the effect of opiate drugs, methadone (Md) and morphine (Mor), on TGFβ1 gene expression was determined. Cells treated with opiates expressed the same levels of TGFβ1 mRNA as untreated cells. Since TGFβ l biological activity can be induced by opiates, the regulation of TGFβ1 gene expression likely involves mechanisms that do not cause changes in mRNA levels.