Clinical evaluation of newly developed oral ampicillin prodrug lenampicillin (LAPC, KBT-1585) applied to patients with superficial purulent infection at a dosage of 750 approximately 1,500 mg daily was conducted. Additionally, as part of the basic study, transition of the compound to the human skin tissue was observed. With regard to transition to human skin tissue in 11 presurgery dermatitis cases, 250 mg or 500 mg of LAPC was administered to 2 approximately 3 hours before surgery. Comparison was made between concentrations in serum and in skin tissue. Results in the case of 250 mg application showed serum concentration to be 1.28 approximately 3.32 micrograms/ml, and in skin tissue, 0.13 approximately 0.82 micrograms/g. At 500 mg, serum concentration was found to be 2.23 approximately 10.05 micrograms/ml, with skin tissue concentration at 0.45 approximately 1.34 micrograms/g. Rate of clinical efficacy in the treatment of the 183 cases of superficial purulent infection was 79.2%. By grouping of the infections (Table 3), high efficacy rates were obtained in the second group, at 85.7%; in the third at 88.9%; and in the fourth group at 96.4%. Evaluation of usefulness from the standpoint of safety was 77.6%. Good results were obtained in the third group with 88.9%; and in the fourth group with 96.4%. LAPC's efficacy rates against individual strains of bacteria in simple infection are as follows: Staphylococcus aureus, 74.6%; Staphylococcus epidermidis, 76.3%; GPC, 100%; anaerobes, 87.5%. In polymicrobial infections the rate was 84.6%. The rate of efficacy against all strains of bacteria was 76.0%. Adverse reactions were found in 13 cases (14 incidences) out of 193. The rate of incidence was 7.3%, with allergic response accounting for 5 cases, digestive tract disorders, 7 cases, and mouth odor, 1 case. There were 5 cases (6 incidences) of abnormal deviation of laboratory findings. In all cases, abnormal deviations were mild and their relation to the drug was unclear.