1. 1. The behavioural effects of ββ′-iminodipropionitrile (IDPN) were studied in chicks and adult fowls. 2. 2. Repeated administration of IDPN (75 mg/kg) for 5 days induced behavioural changes in chicks and adult fowls characterized by excitation, choreiform head and neck movements and circling (ECC-syndrome). 3. 3. Both acute and chronic administration of IDPN induced EEG desynchronization, EMG activation and enhancement of photic-evoked response (PER) in the hyperstriatum and pontine reticular formation while a decrease in PER was observed in the optic tectum. 4. 4. d-Amphetamine (2.5–5 mg/kg), apomorphine (0.1–0.25 mg/kg), piribedil (2.5–5 mg/kg), atropine (2.5–5 mg/kg), hyoscine (2.5–5 mg/kg) and cyproheptadine (0.5 mg/kg) potentiated the circling and choreiform head and neck movements. These activities were antagonized by pimozide (1 mg/kg), physostigmine (0.5 mg/kg) and quipazine (2.5–5 mg/kg). 5. 5. The results suggest that dopaminergic, serotoninergic and cholinergic mechanisms may be involved in IDPN-induced behavioural effects in chicks.