Background Baclofen, a GABA(B) agonist, has been shown to reduce transient lower oesophageal sphincter relaxations (TLESRs), a major cause of gastro-oesophageal reflux disease (GERD). Aim To examine the effect and tolerability of baclofen in GERD patients over a 2-week period. Methods Forty-three GERD patients with abnormal 24-h pH tests were prospectively randomised to receive baclofen or placebo in a double-blind fashion for 2 weeks. Oesophageal manometry, 24-h pH monitoring, and a standard questionnaire was administered, before and after treatment. Results Thirty-four patients completed the study. In the baclofen group there were significant decreases in 24-h pH score (P = 0.020), percent of upright reflux episodes (P = 0.016), percent total time pH <4 (P = 0.003), number of reflux episodes (P = 0.018), number of reflux episodes longer than 5 min (P = 0.016), number of postprandial reflux episodes (P = 0.045), and percentage of time pH <4 (P = 0.003). No significant changes in reflux parameters were noted in the placebo group. Patients receiving baclofen had significantly less belching (P = 0.038), regurgitation (P = 0.036) and overall symptom score (P = 0.004) whereas placebo patients had less heartburn (P = 0.001), chest pain (P = 0.002), regurgitation (P = 0.017) and overall symptom score (P = 0.000). However, there were no significant differences in changes of reflux parameters or symptoms when comparing the two groups. Drowsiness did not limit baclofen use. Conclusions Baclofen was associated with a significant decrease in percent upright reflux by 24-h pH monitoring and a significant improvement in belching, regurgitation and overall symptom score. Baclofen may be more effective in patients with predominantly upright reflux and belching.