SCH 50911, (+)-(S)-5,5-dimethylmorpholinyl-2-acetic acid, a selective, orally-active and competitive γ-Aminobutyric acid B GABA(B) receptor antagonist, binds to GABA(B) receptor with IC50 of 1.1 μM. SCH 50911 antagonizes GABA(B) autoreceptors, increasing the electrically-stimulated 3H overflow with an IC50 of 3 μM.