One can see the nose as a unitary sensory organ that detects odors. This view is extremely reductive within the animal kingdom. Macrosmic animals such as mice rely heavily on olfaction to survive. Their olfactory system is divided in anatomically and functionally distinct subsystems. Sensory neurons in these subsystems express different types of chemoreceptors, use different transduction cascades and contact different area within the brain. The first part of this thesis describes the expression of third type of receptors, the formyl peptide receptors, within one of the mouse olfactory subsystem: the vomeronasal organ. In the second part, we address the role of these immune-related receptors within the mouse olfactory system. Our current hypothesis is based on the literature describing the ability of rodents to avoid sick conspecifics. We used different behavior tests to challenge this hypothesis. Our current data suggest that the VNO is involved in sickness detection and avoidance.