The material produced in the mandibular glands of queen honey bees can be transported by her attendants and causes an inhibition of oogenesis in the workers who cannot make a direct contact with the queen. It seems that the only substance involved in this procedure is 9-oxo-decenoic acid from the queen's mandibular glands. A worker bee from a queenless group of workers shows a variety of behaviour types when it encounters a queen. This consists of avoidance and aggression, offering food, feeding and retinue behaviour and finally negligence. Although most changes of one behaviour type into another occur randomly, the overall pattern can be divided into an initial phase in which avoidance and aggression are frequently observed, a second phase characterized by feeding and retinue behaviour and a final phase in which negligence of the queen dominates. When back in her group of workers this bee functions as substitute queen by attracting the attention of the others, which show principally the same behaviour types to her. This attractiveness of the substitute queen is due to mandibular gland substances from the queen, adhering to the bee's body. Food exchange between the substitute queen and her attendants is mainly directed to the substitute queen. Feeding by the substitute queen is almost always related to the occurrence of aggression towards her. This is opposite to what might be expected when food exchange would be the mechanism by which information about the presence of the queen is distributed among the colony members. When a queen is deprived of her mandibular glands she evokes the same behaviour types in an encountered bee, but the frequency of negligence is higher, whereas feeding and retinue occur less frequently. When back in her group of workers this bee hardly functions as substitute queen, since she is almost treated as an arbitrary bee. Both the attractiveness of the returned worker and the direction of food exchange indicate that sensory perception by means of the antennae of 9-oxo-decenoic acid on the body of the queen or the substitute queen plays a major part in the "queenright" behaviour of the bees.