1. 1. The amino acid, γ-aminobutyric acid (GABA), activates two different receptor types (Bowery et al., 1980; reviewed by Ogata, 1990a). 2. 2. GABA A receptors are bicuculline-sensitive and are coupled to Cl - channels, while activation of bicuculline-insensitive GABA B receptors has been implicated in the modulation of Ca 2+ (Dunlap and Fischbach, 1981) and K + (Gahwiler and Brown, 1985; Inoue et al., 1985a,b; reviewed by Ogata, 1990b) channels. 3. 3. Baclofen is a specific agonist for GABA B receptors (Bowery et al., 1980). In rat sensory neurones, baclofen suppresses the membrane Ca 2+ current ( I Ca) by a mechanism involving a partussis toxin-sensitive G protein (Holz et al., 1986; Scott and Dolphin, 1986). 4. 4. It has been shown that the inhibitory effect of baclofen is more potent on the early portion of I Ca than on the later portion and consequently the rate of I Ca activation is slowed (Deisz and Lux, 1985; Dolphin and Scott, 1986). 5. 5. The mechanisms underlying these GABA B-mediated modulation of I Ca is not fully understood. This article reviews the inhibitory action of baclofen on I Ca in sensory neurones.