Basic fibroblast growth factor (bFGF) extracted from 23 human pituitary adenomas and 2 nontumorous anterior pituitary glands was examined by Western blot analysis to elucidate their molecular forms. Four bands that specifically interacted with anti-bFGF antibody were identified at the regions of 16K, 18K, 22K, and 24K mol wt. These immunodetectable bFGFs were bound to a heparin-Sepharose affinity column and eluted with 1-2 M NaCl. These partially purified tumor extracts could stimulate dose-dependently the growth of FGF-responsive cells. Some tumors contained bFGF with a mol wt of 24 K as a dominant form. In contrast, a major form of bFGF at the region of 18K was identified in the nontumorous anterior pituitary glands. We also addressed the possible presence of FGF receptor mRNA using Northern blot analysis. Many, but not all, human pituitary adenomas were found to contain detectable levels of FGF receptor mRNA with a size of 3.5 kilobases. The present results suggest that the role of bFGF in growth and hormone secretion in human pituitary adenomas should be examined using high mol wt forms of bFGF.