Blood levels of ampicillin (ABPC) were measured in 10 childish patients with heart disease after the rectal administration of KS-R1 at doses of 125 mg and 250 mg. Average blood levels of ABPC at 15, 30 minutes, 1, 2 hours and 4 hours after the administration of KS-R1 were 6.8, 6.9, 3.1, 1.1 mcg/ml and 0.1 mcg/ml with half-life of 0.64 hours in patients of age from 1 year to 4 years 7 months old (dose level 8.9 approximately 13.9 mg/kg, average 10.5 mg/kg), and 5.2, 6.1, 3.4, 1.0 mcg/ml and 0.1 mcg/ml with half-life of 0.65 hours in patients of age from 7 years 10 months to 10 years 7 months old (dose level 8.3 approximately 13.9 mg/kg, average 9.8 mg/kg), respectively. Clinical effective rate (excellent and good) was 87% in 55 childish patients with infections. Bacteriologically, 13 strains (74%) out of 18 strains which were isolated from the patients were eradicated. No severe side effects were observed. Diarrhea was observed in 3 cases.