The effects of systemic administration of the full dopamine D1 receptor agonist A-77636 on acetylcholine release in rat frontal cortex and hippocampus were studied using in vivo microdialysis. Administration of A-77636 (4 μmol/kg s.c.) greatly (>230%) increased both cortical and hippocampal acetylcholine release for more than 3 h; at a lower dose (1 μmol/kg s.c.) A-77636 significantly stimulated cortical but not hippocampal acetylcholine release. The effect of the higher dose of A-77636 on cortical acetylcholine release was blocked by the dopamine D1 receptor antagonist SCH 23390 (300 μg/kg s.c.). These results confirm that stimulation of dopamine D1 receptors facilitates cortical and hippocampal acetylcholine release in vivo, and indicate that these two structures are differentially sensitive to this effect. They also raise the possibility that dopamine D1 receptor agonists may be useful in the treatment of cortical and hippocampal acetylcholine deficit-related syndromes.