Synaptic mechanisms were examined in the pyloric network of the lobster stomatogastric which generate network oscillations in the absence of discrete postsynaptic potentials (PSPs). In normal saline, the unstimulated pyloric network underwent weak bursting in only a few cells. Stimulation of the input nerve, or bath application of the input neurotransmitter dopamine, produced similar vigorous bursting in many pyloric neurons. In saline-containing tetrodotoxin (TTX) plus dopamine, action potentials and corresponding discrete PSPs were blocked, but the underlying slow wave oscillations in network neurons continued. No oscillations occurred in TTX-saline without dopamine. The generation of these nonspiking network oscillations can be explained by the interaction between two synaptic mechanisms which do not produce discrete PSPs: neurotransmitter activation of bursting pacemaker oscillations in a single network neuron, and graded inhibition between network neurons.