Muscimol (MU) was tested on mice for anticonvulsive action against chemical convulsants. 3-Mercaptopropionic acid (3-MP) was more sensitive to inhibition by MU (1.5 mg/kg) than was either pentylenetretrazol (PTZ) or bicuculline (BIC); picrotoxin (PIC) and kainic acid were not measurably antagonized; aminophylline was potentiated. The profile of action of MU closely resembles that of aminooxyacetic acid (AOAA), except that the latter strongly antagonizes kainic acid. MU distinguished more clearly than did AOAA between the action of 3-MP and that of either PTZ or BIC, inasmuch as the differences between the respective potency ratios were larger with MU than with AOAA. The results are consistent with the view that MU acts as a GABA agonist, that GABA antagonism is not a sufficient basis on which to explain the convulsive action of BIC or PIC, and that the antagonism of AOAA toward seizures induced by kainic acid may not be due to an action on the GABA system.