We studied the correlation between microvessel density (MD) and gene expression of vascular endothelial growth factor (VEGF), its receptor (KDR) and basic fibroblast growth factor (bFGF) in 30 human renal cell carcinomas (RCCs). Gene expression assessed by Northern blot hybridization was quantified by a densitometer. Tissue localization of VEGF was assessed by anti VEGF-antiserum staining. MD was measured in tumor tissue sections stained for factor VIII-related antigen. VEGF gene was overexpressed in 18 (60%) of 30 RCCs. Cytoplasm of the tumor cells was stained positively for VEGF staining. Intratumoral expression of KDR gene significantly correlated with that of VEGF gene. bFGF gene expression was very weak, and no tumor overexpressed this gene. The MD in the tumors significantly correlated with the expression intensity of VEGF gene and KDR gene. These results suggest that VEGF contributes to neovascularization of RCCs through a paracrine mechanism, and could be used as a relevant indicator of angiogenesis.