Fibroblast growth factor-1 (FGF-1) and FGF-2 are heparin-binding polypeptides that are potent mitogens for neoplastic cells. In this study, fibroblast growth factor-1 (FGF-1), FGF-2, and fibroblast growth factor receptor-1 (FGFR-1) were immunohistochemically analyzed in 10 patients with pleomorphic adenoma of the salivary gland by using specific monoclonal antibodies. The tumor tissues were histopathologically classified as: tubular, solid, myxoid or chondroid. Both FGF-1 and FGF-2 were immunohistochemically identified in the tumor cells of all histological types. In addition, immunoreactive FGF-2 was also found in the basement membrane of tubular type tumor cells. Conversely, FGFR-1-positive tumor cells were essentially confined to the tubular and solid areas of tumors. Tumor cells in the myxoid and chondroid areas were FGFR-1 immunonegative. These results suggest that the co-expression of FGF and its receptor appears to be related to the proliferative activity of tumor cells in the tubular and solid areas, whereas loss of FGF receptor expression may be associated with the differentiation of tumor cells into myxoid and chondroid tissue types.