Injections of ethanolamine-O-sulfate (EOS) (200 microgram/kg) through chronic indwelling cannulae into the zona reticulata of the substantia nigra in rats produced immediate contraversive turning (away from the injection side). Bilateral injections produced spontaneous stereotyped behaviors including sniffing and biting. Twenty-four hours after the first injection of EOS the rats showed a significantly decreased locomotor response to 1.5 mg/kg D-amphetamine. The spontaneous behaviors elicited following the initial injection of EOS increased both in nature and duration with the second and third injections of EOS, and persevered for 24 h. At this time 1.5 mg/kg D-amphetamine intensified this spontaneous stereotyped behavior. GABA levels were significantly higher in substantia nigra, hypothalamus, corpus striatum and cerebral cortex 24 h following single or repeated (3 x) injections of 200 microgram/kg of EOS into the zona reticulata of the SN. Dopamine levels in the corpus striatum were unchanged 24 h following the EOS treatment except by the injection procedure itself. Control injections into the thalamus produced no turning or stereotypy, nor an enhanced response to 1.5 mg/kg D-amphetamine. GABA levels were, however, significantly higher in the substantia nigra and thalamus 24 h following repeated injections (3 x) of EOS into the thalamus. Results are consistent with the hypothesis that GABA containing neurons comprise part of the efferent output of the corpus striatum and do not act exclusively through a dopaminergic substrate.