Regular oscillations were recorded in olfactory part of the brain (procerebrum) of gastropod mollusk Helix both electrographically and optically. In general, oscillations resembled those in slugs reported earlier. Odor application caused a transient change in the procerebral oscillations followed by appearance of a special pattern. For the first time the evoked potential was recorded in procerebrum and mapped in reference to the area of oscillations. The area of spreading of evoked potential roughly corresponded to the neuropil projection, while the oscillations were recorded in the projection of the cell body layer of procerebrum. The wave of the evoked potential emerged near the place of the olfactory nerve entrance into the procerebrum and propagated via the procerebrum neuropil towards the cell body layer. The evoked potential did not produce a phase-independent wave in rhythmical oscillations.