The mechanisms subserving neophobia and learned aversion have been investigated by recording multiunit olfactory bulb discharges either in hungry rats following food deprivation or in satiated rats. Under the two conditions, rats were stimulated with the smell of their familiar maintenance diet or that of a novel food or of control food-unrelated odor. Responses to the odor of the novel food were tested, following a pairing of the first or the second intake of that food with a LiCl injection, or following its first intake paired with a NaCl control injection. All rats exhibited enhanced level of discharges when they were stimulated in the hungry state with the smell of the familiar food and not when stimulated with the non-alimentary control odor. The hunger to satiety modulation of olfactory bulb discharges, also exhibited in rats tested with the smell of the novel food, previously paired with NaCl, was absent after a LiCl-induced taste aversion to this odor. The small, although significant, modulation observed when the conditioning of aversion occurred with the less novel food is consistent with the view that learned safety prevails upon learned harmfulness. Results are discussed in terms of relations of olfactory bulb electrical responses to odors with food palatability, neophobia and learned aversion.