Adamantinoma of long bones is a rare bone tumour with (immuno-) histological features of epithelial cells, surrounded by various amounts of osteofibrous tissue. Recent studies have indicated that cells with an epithelial phenotype are most probably the malignant element. There is still debate as to whether the fibrous part should be designated as a benign neoplastic element of a biphasic tumour or as a reactive non-neoplastic tissue next to an epithelioid bone tumour. The expression of fibroblast growth factor type 2 (FGF-2), epidermal growth factor (EGF), and their respective receptors FGFR-1 and EGFR, as well as the proliferation marker Ki-67, was studied in both constituents of adamantinoma in serial sections of 25 cases by immunohistochemistry. Expression of FGF-2 and its receptor was present in both constituents of adamantinoma, but predominated in the epithelial component. Expression of EGF and its receptor was restricted to the epithelial component of adamantinoma. Comparing osteofibrous dysplasia (OFD)-like adamantinoma with classic epithelial cell-rich adamantinoma, the expression of FGF-2, EGF, and EGFR was more intense and in a higher percentage of cells in classic adamantinoma. Proliferative activity was found nearly exclusively in the epithelial component. These data further substantiate the hypothesis that epithelial cells constitute the proliferating tumour cell population responsible for the malignant behaviour of adamantinoma. The data indicate that during progression, the epithelial cells acquire expression of FGF-2, EGF, and EGFR, accompanied by a higher proliferative activity. Within the epithelial cell population, there exists an autocrine pathway of growth stimulation. Furthermore, these data point to an interaction between the epithelial and fibrous components, in which the epithelial cells additionally stimulate fibrous cell growth via a paracrine pathway involving FGF-2. 1998