In vivo and in vitro experimental models have suggested a major role for the urokinase-type plasminogen activator (uPA) in tumor cell invasion and metastasis. The uPA proteolytic activity of tumor cells has been shown to be largely determined by the extent of the expression and saturation of the uPA receptor. We have analyzed the expression and cellular localization of both uPA and uPA receptor at the protein and mRNA levels in 33 paired samples of renal cell carcinoma (RCC) and non-tumorous kidney tissue. In comparison with adjacent normal non-tumorous kidney tissues RCC tumor cells modestly overexpressed uPA-receptor mRNA and showed significantly decreased uPA mRNA expression. However, the immunoreactive uPA content of tumor cells was comparable to that of the surrounding normal non-tumorous kidney tissue. Assuming constancy of the uPA-receptor affinity for uPA this indicates that a proportion of the RCC-associated uPA may be derived from an exogenous source and subsequently concentrated at the tumor cell surface via uPA receptor expression. The modest increase in uPA receptor expression may lead to a normalization of uPA antigen content in RCC; however, it is not sufficient to substantially increase tumor tissue-uPA content over the level of normal non-tumorous kidney tissue.