Transforming growth factor (TGF)-β increases the production of the vasoactive peptide endothelin (ET) in cultures of vascular endothelial cells (EC) and vascular smooth muscle cells (VSMC), but the physiologic or pathologic significance of this regulation has not been determined. The present studies test the hypothesis that when EC and VSMC are in direct contact or close proximity, ET expression is, at least in part, dependent on TGF-β. The effects of TGF-β on ET-1 mRNA (Northern analysis and reverse transcription polymerase chain reaction) and peptide (radioimmunoassay) levels were assessed in rat EC and VSMC and vascular organ cultures. TGF-β 2 (1 ng/ml) increased ET-1 mRNA in VSMC and EC plus VSMC cultures and increased ET-1 peptide in EC, VSMC, and EC plus VSMC cultures. TGF-β 2 also increased ET-1 mRNA and peptide in vascular organ cultures. Antibodies that neutralized the activities of TGF-β 1 and TGF-β 2 decreased ET-1 mRNA in EC plus VSMC cultures and in vascular organ cultures. These data indicate that when EC and VSMC are in direct contact or close proximity, TGF-β increases ET expression and active TGF-β is present and promotes ET expression. These data suggest that TGF-β is a determinant of vascular ET expression in vivo, and that TGF-β regulation of ET expression would affect cardiovascular function in health and disease.