In barbiturate anaesthetized cats, dorsal column stimulation inhibited ascending volleys recorded in the antero-lateral spinal fasciculus from electrical stimulation of the contralateral tibial nerve and the excitation of neurones of the dorsal horn by noxious heating of the skin. The inhibition was non-selective. Intravenous bicuculline (0.2-0.6 mg/kg) reduced dorsal column induced inhibition of ascending volleys. Bicuculline but not strychnine, administered electrophoretically from micropipettes, reduced dorsal column induced inhibition of the excitation of dorsal horn neurones by noxious heat. These findings suggest that the inhibition studied was produced by release of gamma-aminobutyric acid. This amino acid may play a role in the clinical suppression of pain produced by dorsal column stimulation.