The transforming growth factor-beta (TGF-beta) cytokine family has important and complex effects on many biologic processes. Mammals have three TGF-beta isoforms which differ in their primary amino acid sequence, receptor binding characteristics, distribution, and function. Characterization of TGF-beta production and localization is critically dependent upon appropriate reagents, including antibodies. We have analyzed the isoform specificity of eight commercially-available TGF-beta antibodies, including one monoclonal antibody and seven polyclonal antibodies. We carried out semi-quantitative Western blot analysis using recombinant TGF-beta1, beta2, and beta3 as targets. We found that sensitivity and isoform specificity are dependent in part upon the presence or absence of reducing conditions. The antibodies tested showed a broad range of sensitivity, with an ability to detect 50 pg to 20 ng. Cross-reactivity with another, incorrect isoform was seen with several antibodies, and ranged from 0.2% to 42%. Nevertheless, we identified TGF-beta antibodies directed against each isoform which provide moderate-to-high sensitivity and specificity when used in Western blot analysis. These results may have relevance for investigators who wish to detect particular TGF-beta isoforms with techniques other than Western blot analysis, particularly when these techniques involve denatured proteins.