Our main finding is that elevator motoneurones do not show sustained firing to intracellular injections of depolarising current pulses in rats anaesthetised with urethane. In contrast, virtually all elevator motoneurones show sustained firing in pentobarbitone-anaesthetised rats. The differences in firing are not associated with significant differences in membrane potential, spike amplitudes, AHP amplitude or duration, input resistance, time constant or rheobase (P greater than 0.06 in all cases). However, there are clear differences in the extent of sag seen under the two anaesthetics and so we tentatively suggest that the anaesthetics may differ in their effects on the inward rectifier.