The calcium binding proteins, parvalbumin, calretinin, and calbindin are found in the ventral respiratory group (VRG) of the medulla. We have shown earlier that parvalbumin cells may be retrogradely labeled from the VRG or from the phrenic nucleus (Alheid et al,SFN 2000). Here we compare the immunohistochemistry of these three proteins with that for the substance P (NK1) receptor which is found in cell bodies of the preBotzinger complex (preBotC), but not in the other compartments of the VRG (Gray et al, Science, 286,1566, 1999). Parvalbumin neurons are labeled extensively within the VRG, particularly in rostral VRG and in the Botzinger complex (BotC). Parvalbumin positive cells are scarce in the pBC and are never co-localized with NK1. Caudal to the BotC is an area that appears to be poor for both parvalbumin and NK1 cells. Calbindin neurons are scattered in the region of the VRG but are scarce or absent from the BotC. Calbindin neurons intermingle, but do not co-localize with NK1 cells in preBotC. Calret...