Brain and pituitary fibroblast growth factors (FGF) have been purified to apparent homogeneity from crude tissue extracts by a three-step procedure, including salt precipitation, ion-exchange chromatography, and heparin-Sepharose affinity chromatography. Brain and pituitary FGF have similar amino acid compositions and are indistinguishable with respect to molecular weight (16,000 by polyacrylamide gel electrophoresis), retention behavior in reversed-phase high-performance liquid chromatography, and recognition by antibodies directed against the amino-terminal sequence of pituitary FGF. Brain FGF preparations purified by heparin-Sepharose contain, in addition to the major FGF molecular species, at least two additional forms of the growth factor, which appear to be very similar by all the above criteria, except for retention in high-performance liquid chromatography.