Between 1996 and 1997 serum and urine levels of basic fibroblast growth factor (b-FGF) in patients with head and neck cancer were measured to answer the following questions: i) Are increased levels of b-FGF in serum and urine detectable in patients with malignant head and neck tumors? ii) Do these parameters correlate with tumor stage and differentiation of tumors? iii) Is there an association between growth behaviour (local or metastatic growth) and b-FGF levels in serum and/or urine? Eighty-nine patients with head and neck cancer as well as 45 patients with diseases unrelated to cancer were investigated. Detectable levels of b-FGF were found in the serum and urine of patients with malignant head and neck tumors. In addition, there was a significant correlation between tumor size and b-FGF levels in either serum or urine. No association of b-FGF concentrations with degree of histologic differentiation and tumor growth behaviour was observed. The results of this study demonstrate that b-FGF levels are elevated in serum and urine of patients with head and neck cancer. These findings suggest an involvement of b-FGF in the formation of solid tumors.