The pyloric network of the stomatogastric ganglion of the lobster Panulirus interruptus is a model system used to understand how motor networks change their output to produce a variety of behaviors. The transient potassium current (I(A)) shapes the activity of individual pyloric neurons by affecting their rate of postinhibitory rebound and spike frequency. We used two electrode voltage clamp to study the modulatory effects of dopamine (DA), octopamine (OCT), and serotonin (5-HT) on I(A) in the anterior burster (AB), inferior cardiac (IC), and ventricular dilator (VD) neurons of the pyloric circuit. DA significantly reduced I(A) in the AB and IC neurons and shifted their voltages of activation (V(act)) and inactivation (V(inact)) in a depolarized direction. These ionic changes contribute to the depolarization and increased firing rate of the AB and IC neurons produced by DA. Likewise, 5-HT significantly reduced I(A) and shifted V(inact) in the depolarized direction in the IC neuron, consistent with 5-HT's enhancement of IC firing. None of the amines evoked significant changes in I(A) in the VD neuron, suggesting that other currents mediate the amine effects on this neuron.