We investigated the action of baclofen, an agonist for GABA(B) receptor, on the dorsal root-evoked inhibitory postsynaptic currents (IPSCs) in substantia gelatinosa (SG) neurons in the adult rat spinal cord slice. Most of the dorsal root-evoked IPSCs in SG were mediated by Adelta fibers. Baclofen (10 microM) reduced the amplitude of Adelta fiber-evoked glycine receptor-mediated IPSCs to 20.9+/-3.0% (n=13), and GABA(A) receptor-mediated IPSCs to 18.6+/-3.4% (n=12) of the controls, respectively. The results further suggest modulatory role of GABA(B) receptor in spinal dorsal horn.