The membrane properties of some inter- and motoneurones in the respiratory and flight systems of the locust Locusta migratoria were characterized during octopamine perfusion by means of intracellular recording techniques. Octopamine induced active membrane properties in these neurones. Plateau-potentials were evoked by brief current pulses or synaptic input in 3 of the identified neurones and endogenous bursting was evoked by prolonged current pulses in one identified interneurone. Hyperpolarizing pulses injected into these neurones either prematurely terminated or suppressed these responses, indicating that these potentials are due to active membrane properties intrinsic to these neurones. Such intrinsic membrane properties have not been described in insects before. Further investigations are necessary to examine whether these properties may play an important role in the generation of rhythmic motor patterns as has previously been demonstrated in many other vertebrate and invertebrate motor systems.