An antiserum was prepared against a synthetic peptide corresponding to the first 29 N-terminal amino acid residues of transforming growth factor beta type 2 (TGF beta 2) from porcine platelets. The anti-TGF beta 2 peptide antiserum appeared to be completely specific for TGF beta 2 in several immunological assays, including enzyme-linked immunosorbent assays, immunoblotting and immunofluorescence experiments. Furthermore, this antiserum completely neutralized the growth inhibitory effect of TGF beta 2 on mink lung carcinoma (ML-CC164) cells and the transforming capacity of this factor on quiescent monolayers of NRK cells in the presence of epidermal growth factor. These data indicate that the N-terminal region of TGF beta 2 may be involved in the biological activity of this growth factor. TGF beta 1 was not recognized by the anti-TGF beta 2 peptide antiserum. The specificity of the anti-TGF beta 2 peptide antiserum for TGF beta 2 appeared to be useful in identifying TGF beta 2 produced by different cell systems and will be helpful in determining possible functional differences between TGF beta 1 and TGF beta 2.