Nitric oxide (NO) has been implicated in central olfactory processing. In the land slug Limax, injection of L-NAME, a NO synthase inhibitor, blocks appetitive olfactory conditioning and discrimination of odors after aversive conditioning. However, direct evidence for NO-mediated effects in the CNS during olfactory stimulation has been lacking. We recorded odor-evoked neural responses in the procerebral (PC) lobe of Limax in an isolated nose-brain preparation. The frequency of local field potential (LFP) oscillation in the PC lobe increased in response to olfactory stimulation, and this was blocked by perfusion with L-NAME. Optical recording of the PC lobe using a voltage sensitive dye revealed traveling waves of neural activity in the resting state, and olfactory stimulation switched the traveling waves to synchronous activity. L-NAME blocked the odor-evoked switching of waves to synchrony. We recorded the NO concentration in the PC lobe using an NO sensitive electrode, and observed an increase in NO concentration following olfactory stimulation. These results suggest that NO released by olfactory stimulation modulates the network dynamics in two ways: NO increases the frequency of oscillation and synchronicity of activity. These effects of NO may underlie gating of information flow and synaptic plasticity.