Honey bees display a dramatic but incomplete reproductive division of labor. Colonies consist of several thousand sterile workers, and a single reproductive queen. Typically, only a small percentage of workers (~0.01%) in a queenright colony have active ovaries. However, in the absence of a queen, the ovaries of young workers can become activated and they can lay unfertilized eggs that develop into drones. The phenomenon of worker reproduction has been considered in evolutionary theories of worker-queen conflict, kin selection, and altruism. However, the molecular basis of worker reproduction has not been considered. Here we describe a series of microarray experiments comparing the brains of age-matched virgin queens, workers without ovaries, and workers with fully developed ovaries. Several hundred genes were found to be significantly different between the three groups; these can be separated into genes specifically associated with worker ovary development, reproduction, and caste. Interestingly, the global gene expression pattern in the brains of workers with ovaries lies intermediate between sterile workers and virgin queens. These results suggest that the genetic mechanisms underlying reproduction are conserved between workers and queens, but are activated to a lesser extent in workers.