The aims of the present study were to compare effects of sodium alginate and the antacid magaldrate anhydrous in adults with gastroesophageal reflux (GOR) symptoms. Patients with heartburn and/or acid regurgitation for at least 3 days in the week before the study started (n=203) were randomized to receive a single dose of sodium alginate or magaldrate anhydrous at the onset of symptoms during a 3-day run-in period. Patients with symptoms during the run-in (n=191) were rerandomized to receive a 14-day treatment with either drug given as four daily doses. A speed of action < or =30 min was significantly more frequent among patients in the alginate group (49.4% vs. 40.4%; P=0.0074). A trend toward a more prolonged duration of action (median: 16.5 vs. 12.7 hr) and a greater sum of the symptom intensity difference (median: 40.0 vs. 31.0) was observed in the sodium alginate group. Total disappearance of symptoms was reported in 81.6% and 73.9% of patients in the sodium alginate group and magaldrate group, respectively. We conclude that sodium alginate was faster than magaldrate in relieving GRO symptoms and showed a tendency toward a more prolonged duration of action and a higher level of efficacy.