A protocol was developed to isolate and enrich single renal proximal tubular cells, performing the following steps: in situ kidney perfusion; isolation of renal tissue pieces by collagenase digestion; selective enrichment of proximal tubular fragments by Percoll gradient centrifugation; and isolation of single proximal tubular cells by digestion of proximal tubular fragments with trypsin. The mean enrichment rate, determined by the glucose-6-phosphatase staining method, was 78.9% with a mean cell viability of 93.8%. After modification of the comet assay protocol, genotoxicity in proximal tubular cells could be investigated. A dose-dependent genotoxic effect of ethyl methanesulphonate in these cells was proven.