BACKGROUND AND AIMS: Laperarnide is an esteblished treatment regimen for acute diarrhea. The prodrug loperamide oxide is converted to loperamide by the anaerobic bacteria in the lower gastrointestinal tract. When loperamide oxide with a low dose and a low plasma concentration was used, it was expected to obtain similar antidiarrheal effect as using loperamide. The incidence of adverse reactions might be reduced with the use of loperamide axide. According to a few reports from other nations, loperamide oxide was me effective than placebo. This study was perfomed to canfirm the antidiarrhea1 effect and the safety of loperamide oxide in Korean patients with acute diarrhea. Methods, Loperamide oxide (1 mg tablets) was compared with placebo in a double-blind placebo-contmlled treatment of acute diarrhea of 140 Korean patients from 5 university/general hospitals located at or around Seoul. RESULTS: We completed such trial for one hundred and eleven (56 of placebo group and 55 of active drug group) cases. Number of consumed tablets were significantly less in active drug group (p=0.0005). The first relief was more frequently experienced (p=0.0032) and time taken upto the first relief was shorter (p=0.0471) in loperamide oxide treated group than in placebo group. Early event was more frequently experienced (p= 0.0001) in loperamide oxide group. Complete relief was more frequently experienced (p=0.0032) but not significantly shorter in loperamide oxide group. Both the patieats' visual analogue scale (p=0.0007) and the investigators' global assessment (p=0.0011) of the treatment significantly favored the loperamide oxide over placebo. No evidence of adverse reactions related to this drug was experienced. CONCLUSIONS: These results suggest that loperamide oxide can be used safely and effectively for the relief of acute diarrheal symptoms.