Cell adhesion to extracellular matrices is mediated by a set of heterodimeric cell surface receptors called integrins that might be the subject of regulation by growth and differentiation factors. We have examined the effect of transforming growth factor-βl (TGF-β1) on the expression of the very late antigens or αβ₁ group of integrins in human cell lines. The six known members of this family share a common β₁ subunit but have distinct α subunits that confer selective affinity toward type I collagen, fibronectin, laminin, and other as yet unknown cell adhesion proteins. Using a panel of specific antibodies and cDNA probes, we show that in WI-38 lung fibroblasts TGF-β1 elevates concomitantly the expression of α₁, α₂, α₃, α₅, and β₁ integrin subunits at the protein and/or mRNA level, their assembly into the corresponding αβ₁ complexes, and their exposure on the cell surface. The rate of synthesis of total α subunits relative to β₁ subunit is higher in TGF-β1-treated cells than in control cells. The characteristically slow (t_½ ∼ 10 h) rate of β₁ conversion from precursor form to mature glycoprotein in untreated cells increases markedly (to t_½∼3 h) in response to TGF-β1. The results suggest that in WI-38 fibroblasts the β₁ subunit is synthesized in excess over α subunits, and assembly of β₁ subunits with rate-limiting α subunits is required for transit through the Golgi and exposure of αβ₁ complex on the cell surface. TGF-β1 does not induce the synthesis of integrin subunits that are not expressed in unstimulated cells, such as α₄ and α₆ subunits in WI-38 fibroblasts. However, α₄ and β₆ subunits can be regulated by TGF-β in those cells that express them. The results suggest that TGF-β regulates the expression of individual integrin subunits by parallel but independent mechanisms. By modifying the balance of individual αβ₁integrins, TGF-β1 might modulate those aspects of cell migration, positioning, and development that are guided by adhesion to extracellular matrices.