In order to determine whether infusion of antibiotics into the urinary bladder, which is frequently used in clinical practices, is really effective, DKB was given by this route in 14 cases undergone transurethral operations. The patients were divided into two groups : one group received the drug at a dosage of 200 mg, and the other 400 mg. Observations were made on changes with time in blood drug levels, retaining time in the urinary bladder, recovery rate and absorbability from the urinary bladder. Moreover, a comparison was made with transitional changes in the blood levels following systemic administration of DKB, and significance of infusion therapy against MIC of Pseudomonas aeruginosa was investigated. The results are given below.<BR>1. In the pilot study, 3 healthy male adults were given an infusion of 200 mg of DKB in the urinary bladder. The miximum blood level of 0.273μg/ml was reached within 1/2 hour, which fell gradually in function with time. At 120 minutes after administration, 0.193μg/ml of DKB was found, with recovery rate of 79.0%.<BR>2. Patients with lower urinary tract infections secondary to transurethral operations were treated with 200 mg of DKB, which was given as an infusion into the urinary bladder, and determined for blood levels of DKB. At 0.5, 1, 1.5 and 2 hours after administration, mean blood levels of 1.31±0.44, 1.09±0.23, 1.07±0.37 and 0.95±0.38μg/ml, were found respectively, with a recovery rate of 49.0±13.5%.<BR>3. Following an administration of 400 mg of DKB, the mean blood levels at 0.5, 1, 1.5 and 2 hours after administration were 2.08±0.60, 1.81±0.52, 2.07±0.14 and 1.79±0.15μg/ml respectively, recovery rate being 62.8±16.9%.<BR>4. The absorption of DKB from the urinary bladder was increased in patients with lower urinary tract infections, since it was shown that the highest blood levels attained in treated groups (200 and 400μg/ml) were 4.8 and 7.7 times, respectively, as high as those recorded for the control group and that in 400 mg group blood levels were 1.6 times higher than those of 200 mg group.<BR>5. From the fact that, when given as an infusion into the urinary bladder, blood levels once reached showed only a slight decrease with time and that remarkable increase in penetration into the tissue of urinary bladder was indicated from the recovery rate obtained in this study, we believe that this administration route is quite promising in the treatment of lower urinary tract infections.