The patch-clamp technique has been used to investigate single-channel and whole cell conductances in freshly isolated rat hepatocytes. Whole cell experiments, with high (144 mM) intracellular and extracellular potassium as the principal conductive species, show some variation between cells in the current-voltage relationship (mean whole-cell conductance at physiological potentials being 2.7 nS). This may suggest functional heterogeneity of cells. The most common finding is that the current-voltage relationship shows inward rectification. This is reflected in cell-attached single-channel recordings in which channels displaying strong inward rectification and K+ selectivity are seen. The channels show a mean inward conductance (with 144 mM potassium in the pipette) of 44 pS and an outward conductance of 23 pS. The open probability is not voltage dependent, and the channels do not exhibit calcium dependence. The channels are quite different from others described in hepatocytes, but they show marked similarities to channels recently described in renal epithelial cells. Current-voltage relationships in the whole cell mode exhibit an increase in slope conductance at large hyperpolarizing and depolarizing potentials.