Aminopeptidase N (APN) and dipeptidylpeptidase IV (DPIV) are transmembrane type II molecules widely distributed in mammalian tissues. In recent years, the interest in cell surface peptidases has increased considerably because, among other things, several reports indicate roles of ectopeptidases in tumour cell metastasis. Investigations into the regulation of APN and DPIV on tumour cells are rare. We report, for the first time, that IL-4 and IL-13 can up-regulate protein expression as well as enzymatic activity of both the peptidases on renal carcinoma cells and renal tubular epithelial cells in culture. The analysis of mRNA by competitive polymerase chain reaction (PCR) confirmed our results with respect to the APN increase at the level of gene expression. IL-1 beta and tumour necrosis factor-alpha (TNF-alpha) augmented the IL-4-induced effect with respect to APN but not to DPIV. A 5-day incubation with interferon-gamma (IFN-gamma) increased protein expression, especially of APN and, to a lesser extent, also of DPIV, whereas no significant increase in enzymatic activity could be observed. Small concentrations of transforming growth factor-beta 1 (TGF-beta 1) inhibit the expression and enzyme activity of DPIV. IL-6, IL-7, IL-10 and granulocyte-macrophage colony-stimulating factor (GM-CSF) have been found to be without any effect on APN and DPIV. For a prospective therapeutic regimen with T cell-derived cytokines it has to be considered that--besides their effect on tumour cell growth--cytokines might affect surface ectopeptidases involved in tumour cell adhesion processes. The inhibition of APN and DPIV could be a new approach to suppression of cancer spread.