The effect of temperature on sodium channel function was examined in GH(3) cells, using the whole cell patch-clamp methodology. Specific parameters examined were current-voltage relationships, activation time, and inactivation time. For the temperature range studied, 23-37 degrees C, there was no change in the current-voltage relationship. A linear response to temperature was seen in the inactivation time constant, tau(h). The activation time constant, tau(m), was clearly nonlinear, with a sharp discontinuity at 28 degrees C. This nonlinearity was especially evident at lower membrane voltages. These findings are consistent with the hypothesis that membrane structural changes, which occur during the thermotropic phase transition, are capable of influencing the function of the intramembranous portion of the channel. Caution should, therefore, be exercised in extrapolating data on channel function obtained at room temperature to physiological temperatures.