The bulbus olfactorius of the rabbit provides an easily accessible brain structure with well-ordered layers of granule cells. Slices of granule cell layers have been utilized for intracellular recordings using microelectrodes with bevelled tips of 0.11-0.12 microm diameter. Among the recorded changes in membrane potential most frequent are groups of 2-13 wavelets increasing continuously in amplitude until finally an impulse is discharged on top of a wave. Further, regular sinusoidal rhythms have been observed. As the slow-wave activity disappears after treatment with inhibitors of intermediary metabolism, such as iodoacetate or malonate, the rhythmic potential changes in granule cells appear to be of metabolic origin.