Two endothelial cell growth factors (ECGF) have been purified from bovine brain and termed alpha- and beta-ECGF [Burgess, W. H., Mehlman, T., Friesel, R., Johnson, W. V. & Maciag, T. (1985) J. Biol. Chem. 260, 11389-11392]. Amino acid sequence analysis indicates that beta-ECGF represents a 20 amino acid amino-terminal extension of alpha-ECGF and a 14 amino acid amino-terminal extension of acidic fibroblast growth factor. These data indicate that both alpha-ECGF and acidic fibroblast growth factor may be derived from beta-ECGF by posttranslational processing. Analysis of the amino-terminal 14 residues of beta-ECGF by fast-atom-bombardment mass spectrometry established the amino acid sequence of this region and the identity of the blocking group at the amino terminus (acetyl).