When queenless honeybees, Apis mellifera, rear new queens, the relative frequencies of subfamilies found in the queen and worker brood are often very different, suggesting that certain subfamilies are reproductively dominant. At least two mechanisms could account for the observed differences in queen and worker broods. First, kin selection theory predicts that if honeybee workers are able to distinguish levels of relatedness, they should act nepotistically by favouring super-sisters over less-related half-sisters during emergency queen rearing. Alternatively, selection might result in royalty alleles that make their possessors more favoured for rearing as queens. Documented genetically based tendencies to rear queen or worker brood might interact with either of these mechanisms. To determine which of these effects might best explain reproductive dominance, we removed brood from the queenright section of one colony and offered it to the queenless section of the same colony and to three unrelated queenless colonies. We used two microsatellite loci to determine the paternity of queen and worker brood reared by these colonies. Variance in the proportions of subfamilies in queen and worker brood was greatest when the rearing bees were related to the brood. The results suggest that nepotistic interactions are more important than royalty alleles or other factors in causing reproductive dominance, but that there are complex interactions between the genotype of the nursing workers, and the genotypes of the larvae favoured for rearing as queens. Copyright 1999 The Association for the Study of Animal Behaviour.