88 unselected patients with acute pancreatitis entered a randomized clinical trial comparing the therapeutic efficacy of fasting alone, nasogastric suction and fasting plus cimetidine. The disease was mild to moderate in all but 3 cases, and cholelithiasis was the main etiological factor. The number of treatment failures and complications, and the clinical outcome were similar in the three groups. However, when compared to fasting alone, nasogastric suction was shown to delay the resumption of bowel activity a mean of 11 h (p less than 0.05), prolong the duration of pain a mean of 20 h (p less than 0.01), increase analgesic needs (pentazocine lactate) a mean of 64 mg (p less than 0.05), and lengthen hospital stay a mean of 2 days (p = NS). In conclusion, cimetidine has no beneficial effects in acute pancreatitis. It is suggested that fasting alone be initially used as the simpler, safer and more economical therapy. Nasogastric suction should be reserved for patients presenting with intestinal ileus, a situation that occurred in 1 out of every 8 cases in the present series.