Cultures of human proximal tubule cells were exposed to elevated concentrations of glucose and dome formation was assessed over a 22 day period of growth. Cultures grown on 5.5 mM glucose formed five domes per microscopic field while those exposed to elevated glucose concentrations (11.0 mM to 27.5 mM) formed only two to three domes per field. The areas of the domes formed by the cells grown on elevated glucose concentrations were reduced as compared to those formed on 5.5 mM glucose. An analysis of the electrical properties of cells grown on elevated glucose concentrations by Ussing chamber technique disclosed a marked reduction in potential difference, short circuit current, and resistance compared to cells grown on 5.5 mM glucose. Routine ultrastructural analysis disclosed that cells grown on elevated glucose concentrations appeared to have fewer tight junction complexes. Further examination utilizing freeze fracture methodology demonstrated that cells grown on elevated glucose concentrations averaged two to three sealing strands per junction as compared to an average of five sealing strands for cells grown on 5.5 mM glucose. The cells grown on elevated glucose concentrations were also noted to possess a greater number of gap junctions. These results demonstrate that elevated glucose concentrations can alter the paracellular route, and possibly the transcellular route, of transport regulation in cultured human proximal tubule cells.