Primary cultures of mammalian proximal tubules (PT) can be established in serum-free, hormone-supplemented media. These cells attain confluence, demonstrate morphological polarity and exhibit vectorial fluid transport. Primary cultures of rabbit PT cells retain the transport properties of the parent cells and exhibit Na+-H+ exchange, Na+-Ca2+ exchange and Na-glucose co-transport, the latter process having kinetic properties comparable to those described for the late proximal tubule. Glucose which enters the cell via the luminal Na-glucose co-transport system undergoes metabolism to CO2; it is not clear whether this glucose oxidation, which is minimal in PT cells under physiological conditions, is due to selection of a specific cell type or to the nature of the culture conditions. Confluent, quiescent PT cells in culture can be induced to hypertrophy by addition of supraphysiological concentrations of insulin, PGE, and hypertonic NaCl; each stimulus also leads to an early increase in Na+-H+ antiport suggesting that this transport process may be causally related to the process of cell growth. The primary culture thus represents a promising model for future studies on the cellular events which govern the process of cell hypertrophy.