ABSTRACT.Worker bees recently denied access to their colony expose their Nasonov glands, thereby releasing pheromone, at the entrance to their hive. Odours of the following induced this response: empty comb, purified beeswax, honey, pollen, propolis, a live queen, the (E)‐9‐hydroxy‐2‐decenoic acid component of a queen's mandibular glands, live drones and workers, inert material on which workers had walked inside the hive, and synthetic Nasonov pheromone. The total odour of a foreign colony also induced worker bees to expose their Nasonov glands but was less effective than the odour of their own colony. Odours of the following were not effective: the (E)‐9‐oxo‐2‐decenoic acid component of a queen's mandibular glands, recently killed drones and workers, worker brood (eggs,