The functional relation between the olfactory bulb and the mesencephalic reticular formation (RF) was studied in curarized rabbits. The results obtained in the acute experiment were confirmed in the chronic experiment.1. High frequency stimulation in the RF suppressed the intrinsic and the induced waves of the olfactory bulb. Peripheral arousal stimuli were sometimes effective in causing a similar changes in the olfactory activity.2. The excitable spots suppressing the activity of the bulb were distributed diffusely in the RF. They were also found to extend in the hypothalamus.3. RF stimulation failed to modify the negative wave potential of about 40 msec duration evoked in the bulb by electrical stimulation of the olfactory mucosa.4. Complete destruction of the olfactory mucosa and section of the anterior commissure were unable to influence the suppression of the olfactory activity due to RF stimulation. On the other hand, neuronal isolation of the bulb abolished the reticular influence.5. In contrast to the neocortical EEG, the olfactory activity failed to show a release phenomenon upon acute destruction of the RF.6. In the chronic experiment peripheral arousal stimuli were found to suppress the intrinsic activity of the olfactory bulb in the same manner as in the acute experiment.A part of the expense of this work was defrayed by a grant of the Ministry of Education.