1. Pharmacokinetic study. Micronomicin (MCR) was administered by intravenous drip infusion at a dose of 180 mg to each of 3 advanced aged patients (average: 77 years). Peak serum concentrations of the drug reached levels ranging from 16.0 to 22.2 micrograms/ml (average 18.8 +/- 3.2 micrograms/ml). In 2 cases with normal renal functions, T 1/2 of MCR was 2.2 approximately 2.5 hours, whereas it was 4.3 hours in a case with a slight renal impairment. No accumulations nor adverse clinical reactions due to the drug occurred in treatment at a dose level of 360 mg daily for 5 days in each of the 2 patients. Also, no abnormal values were noted in beta 2-MG, NAG, creatinine in blood and urine before or after the treatment in any of the above 3 patients. 2. Clinical study. MCR was administered to 26 patients with chronic and complicated urinary tract infections (CC-UTI). Twenty-four patients were treated each at a dose level between 240 and 360 mg daily for 5 days. Clinical efficacy was evaluated for 25 evaluable cases based on the UTI committee's criteria; excellent responses were observed in 4, moderate responses in 14 and poor responses in 7, thus, the rate of efficacy was 72%. 3. Safety. No side reactions were encountered nor clinical abnormal values observed in peripheral blood, in renal, liver functions. 4. Conclusion. The MCR was a highly effective and a safe drug in treatment of CC-UTI including cases of advanced aged patients at a dose in a range of 240 approximately 360 mg per day for 5 days administered by intravenous drip infusion. Appropriate dose levels, however, should be individually established for cases with renal impairment where the excretion of the drug may be retarded.