The resting membrane potential, E(m), and the cell input resistance R(i)n(p), of cultured human Chang liver cells were measured using the single electrode 'double-pulse' current clamp technique, following exposure of the cells to the insecticide DDT (20 μM). In control (unexposed) cells, the mean E(m) was -24 mV, and the mean R(inp) was 30 MΩ. Neither parameter was significantly impaired after 1 h of cell exposure to DDT. But after 7 and 48 h, the E(m) was depolarized by 15 and 25 mV, respectively, in parallel with a decrease of the cell input resistance. The strongly time-delayed effect of DDT on Chang liver cell membranes may indicate a mode of interaction different from excitable membranes.