Cell lysates of two established human tumor lines, a medulloblastoma (TE671), and a rhabdomyosarcoma (RD), contain mitogenic activity which elutes from heparin-Sepharose under conditions typical of class 1 heparin-binding growth factors, such as acidic brain fibroblast growth factor. The presence of this class of mitogen in both cell lines was confirmed by their chromatographic behavior on reversed-phase C3 columns, and by the ability of heparin to enhance their mitogenic activity. Using a specific synthetic DNA probe, RNA's were isolated from both cell lines by hybridization-selection, translated in vitro, and translated proteins affinity fractionated on heparin-Sepharose. The results demonstrate that TE671 and RD cell lysates contain mRNA's for mitogens related to acidic brain fibroblast growth factor, and also suggest that high molecular weight proteins exist that are closely related to, or are precursor forms of, the class 1 mitogens.