Mushroom bodies (MBs), which are thought to represent centres of multimodal processing and integration in arthropod brains, are most evolved in social Hymenoptera. Experimental evidence suggests that they are involved in learning and the formation and storage of memory. In the honey bee (Apis mellifera) the MBs undergo an internal structural reorganisation associated with behavioural development. We here show that the expression of a recently discovered, highly conserved royal jelly protein (RJP-3) is concentrated in a defined population of the Kenyon cells (intrinsic neurons) in honey bee MB. Thus, in addition to their poorly understood role via the digestive system, RJPs may have a novel, previously unsuspected function in the brain. The restricted distribution of RJP-3 message within the MBs supports the view that the Kenyon cells, despite their isomorphic appearance, are divided into functionally distinct sub-compartments.