Aberrant autocrine control by peptide growth factors is a possible mechanism by which disordered regulation of cell proliferation may occur. The authors used the C6 glioma cell line as a model to study the role of basic fibroblast growth factor (bFGF) in tumor growth by transfection with bFGF complementary deoxyribonucleic acid in both the sense and antisense orientation. Clones with high messenger ribonucleic acid expression of the sense construct have increased proliferation in cell culture and increased levels of intracellular and extracellular bFGF. Clones with high expression of the antisense construct show decreased proliferation in culture and reduced levels of immunologically detectable bFGF.