The effect of the GABA(B) receptor agonist baclofen, a potential treatment for gastroesophageal reflux, on gastric emptying has not been determined. The effect of 1-4 mg/kg baclofen on liquid and solid gastric emptying in mice was evaluated by noninvasive [13C] breath tests. Baclofen accelerated gastric emptying of solids but delayed emptying of liquid, suggesting that it may have differential effects on proximal and distal stomach emptying.