Three-year post-marketing surveillance (PMS) on midecamycin acetate dry syrup from July, 1985 through April, 1988 resulted in collection of reports on 12,169 patients. Among these, a total of 66 patients (0.54%) with side effects were reported. The main side effects caused by this drug were gastrointestinal and skin appendages disorders. They included diarrhea, abdominal pain, eruption and others. Side effects, which had not been observed up to the approval were itchiness and multiple erythema. None of these side effects were serious. When the drug was administered to 26 patients hypersensitive to beta-lactam agents, no allergy symptoms developed. Based on these results, midecamycin acetate dry syrup can be evaluated to be a highly safe macrolide in clinical use.