On eight volunteers with reduced kidney function, 1 g of carbenicillin indanyl sodium was administered orally for the single dose studies and was given orally in a dose of 1 g every 6 h for 7 days for the multiple dose studies. The patients were divided into two groups according to their kidney functions: group I moderately impaired and group II severely impaired. In the single dose studies, the mean peak level was 12.6 μg/ml for group I and 26.9 μg/ml for group II. In the multiple dose studies, the drug tended to accumulate in group II, but the level obtained in group II did not exceed more than 300μg/ml. In the single dose studies, the mean peak level in the urine was 1,478.5 μg/ml for group I and 350.0 μg/ml for group II. In the multiple dose studies, despite the multiple dose regimen, the level obtained from group II patients only transiently exceeded more than that which will effectively inhibit the growth of Pseudomonas, Klebsiella and Enterobacter. In the single dose studies, the mean cumulative amount excreted in the urine within 24 h was 314.2 mg for group I and 120.1 mg for group II and the difference between both groups was significant (p < 0.05). For the multiple dose studies, the amount was 278.0 mg for group I and 127.2 mg for group II, respectively. The total amount excreted in the urine within 24 h and the serum level obtained 6 h after ingestion of 1 g of carbenicillin indanyl sodium was correlated to the creatinine clearance and the rate of PSP excreted in the urine within the first 15 min of the test.