Expression of the various isoforms of transforming growth factor-beta (TGF-beta) is differentially controlled both in vivo and in vitro. Characterization of the molecular mechanisms governing expression of TGF-beta isoforms now provides a basis for understanding the selective regulation of expression of the TGF-beta s by a variety of factors including oncogenes and tumor suppressor genes. In addition to transcriptional control, data suggest that expression of TGF-beta s is also regulated posttranscriptionally. Regulation of TGF-beta s by steroids and retinoids appears to involve predominantly posttranscriptional mechanisms. Identification of these mechanisms may contribute to the understanding of the regulatory events controlling cellular proliferation and differentiation by TGF-beta s and steroids/retinoids.