We report on the use of several proximal tubular cell (PTC) surface markets and corresponding antibodies in fluorescence-activated cell sorting (FACS), and their ability to identify and flow sort cells of defined proximal tubular origin (S1S2S3) or of defined proximal subsegmental origin (S1S2 only/S3 only). We tested monoclonal/polyclonal antibodies directed against five different surface peptidases [leucine aminopeptidase (LAP), neutral endopeptidase 24.11 (NEP), dipeptidyl peptidase IV (DPPIV), aminopeptidase A (APA) and gamma-glutamyl transferase (gamma-GT)], the S3 segment-specific marker intestinal type alkaline phosphatase (iAP) and an S1S2 marker (TN20-antigen), originally proposed as a surface marker for interstitial fibroblasts. Segmental (proximal tubular vs. distal tubular) and proximal subsegmental (S1S2 vs. S3) expression of all five surface peptidases and TN20 antigen were first assessed by comparing immunohistochemical staining on normal human kidney tissue with staining for well-known segment-specific differentiation markers (intestinal type alkaline phosphatase, Tamm-Horsfall protein) on adjacent sections. All five peptidases were found to be expressed to a certain degree in all subsegments (S1 S2 and S3) of the proximal nephron, whereas expression was never seen in the more distal parts of the nephron. Flow cytometry was performed on cells obtained following gradient purification of collagenase-digested human renal tissue. Labeling cells for expression of LAP, NEP or DPPIV resulted in high yields of specifically labeled PTC (S1S2S3 origin). Labeling with anti-LAP resulted in the clearest distinction between positive and negative cell subpopulations, and therefore LAP was considered the best PTC marker for use in FACS. iAP histochemical staining on sorted cells showed that flow sorting with monoclonal antibody (moAb) 250 (anti-intestinal type alkaline phosphatase) allowed sorting of S3 cells with > 90% purity. Likewise, moAb TN20 enabled us to obtain a highly purified S1S2 population as confirmed by the absence of iAP on sorted cells.