The possibility that displacement activities might be consequences of stress-induced humoral responses was investigated. Adrenocorticotropic hormone and glucose were injected into the brain ventricles of unrestrained domestic pigeons. ACTH leads to an increased frequency of yawning and headshaking and glucose to a decrease in arousal. It is concluded that these behavioural responses correspond partly with the displacement activities shown by birds. The role of the cerebrospinal fluid as a mediator of behaviourally active substances is discussed.