In a group of 94 duodenal ulcer patients consecutively studied and followed-up for 1 year, subjects with maximal acid output (M.A.O.) above 60 mmol/hour (mostly heavy-smoking men), were found to relapse more frequently than those with lower M.A.O. values (72.2% versus 27.6%; p less than 0.0005). A significantly higher relapse rate was also detected in patients treated with maintenance dosages of effective antisecretory drugs (cimetidine, ranitidine, pirenzepine) and presenting M.A.O. over 60 mmol/hour. It is yet to be established whether an alternative therapeutic regime may prove effective in preventing ulcer recurrence in patients with gastric hypersecretion.