BACKGROUND This was a randomized, double-blind, placebo-controlled, multicentre, parallel group, dose-ranging trial of ranitidine tablets for relief of episodic heartburn. Adult out-patients who reported heartburn relieved by antacids at least seven times per week were eligible. METHODS Patients who successfully completed a 1-week single-blind placebo run-in phase and who did not achieve adequate relief in more than 50% of heartburn episodes were randomized to a 1-week, double-blind treatment phase during which they received ranitidine doses of 25, 75 or 125 mg, or placebo. RESULTS Of 577 patients randomized, 566 had at least one evaluable heartburn episode and were included in the intention-to-treat analysis. All three ranitidine doses were statistically significantly superior to placebo in providing overall episodic heartburn relief for the first episode (P < 0.002), last episode (P</=0.004), and all episodes combined (P < 0.001). The ranitidine 75 mg and 125 mg doses provided sustained relief (relief within 60 min of dosing that lasted throughout the 4-h evaluation period) to a greater proportion of patients for each individual episode (43-56% for 75 mg and 42-57% for 125 mg) than the ranitidine 25 mg dose (35-50%) or placebo (21-29%). The incidence of adverse events was similar in all treatment groups. CONCLUSIONS All three ranitidine doses (125, 75 and 25 mg) are safe and superior to placebo in providing adequate relief for heartburn. Ranitidine's onset of relief was progressive and clearly present by 30 min as shown by statistically significant differences for the 75 mg dose when compared to placebo. Similarly, patients treated with ranitidine 75 mg and 125 mg consumed statistically fewer rescue antacids than placebo-treated patients for the first episode. All three doses were well tolerated, with adverse event profiles similar to those of placebo.