Postsynaptic field potential was elicited in the central nucleus of the rat inferior colliculus after electrical stimulation to the lateral lemniscus. The inhibitory action of locally applied GABA on the potential was blocked by the systemic administration of picrotoxin, a GABA A antagonist (2.5 mg/kg, i.p.). After the administration of picrotoxin, the tetanic stimulation of 50 Hz for 20 s increased the amplitude of the field potential to over 120% of the original level in 10 min; this was maintained for 40 min, and formed the long-term potentiation (LTP). The tetanic stimulation alone, however, failed to enhance the amplitude. Thus, LTP was induced in the inferior colliculus only when GABAergic action was depressed.