Resting potentials in Apis mellifera and Drosophila melanogaster flight muscles decrease with falling temperatures. When resting potentials fall to between -37 and -45 mV they activate a final burst of spontaneous muscle action potentials (MAPs). This final burst of MAPs marks the beginning of chill-coma for each species. The temperature at which the final burst occurs for D. melanogaster (7.0+/-0.9 degrees C) is significantly lower than that of A. mellifera workers (10.6+/-1.2 degrees C), queens (10.2+/-0.8 degrees C), and drones (12.8+/-0.8 degrees C). Prior to chill-coma, MAP amplitudes decrease and durations increase with falling temperatures in both A. mellifera and D. melanogaster. The rate of these changes and the temperatures at which they occur appear to be related to the rate of decline in each species' resting potential. These results suggest that insect chill-coma varies with a species' ability to maintain its resting potential at low temperatures.