Carbenicillin was evaluated in 46 infections, mostly urinary tract and a few systemic, in the majority due to Pseudomonas aeruginosa. Of 39 urinary tract infections 17 were chronic pyelonephritides, 5 acute pyelonephritis, 15 cystitis, 1 urethritis and one kidney stone with infection. 30 were due to Pseudomonas alone, 1 to E. coli, 1 to Proteus, 1 to Staphylococcus, 3 to a combination of Pseudomonas and Proteus or E.coli, 2 to Proteus and E.coli and 1 to Klebsiella and Enterobacteriaceae. Of the 39, 22 showed excellent immediate clinical and bacteriological response, 12 improved and 5 failed. All 3 respiratory tract infections and one otitis (chronic) did not respond, perhaps due to insufficient dosage. Two septicemias showed excellent response with high doses (30 g daily). One had extensive burns and a critical condition. The other was in a more severe state: Pseudomonas septicemia with characteristic rash was superimposed on a severe icterus (mainly hepatocellular, partly hemolytic) with a severe sickle cell anemia crises in a girl with previous splenectomy. Carbenicillin administration was followed by dramatic effect and proved lifesaving. Carbenicillin is a useful agent for Pseudomonas and other Gram-negative infections. Urinary tracts respond fairly easily and patients previously resisting other treatments were finally cured with carbenicillin in moderate doses (3 g daily). Systemic infections require high doses (up to 30 g daily), sometimes assisted by the oral use of probenicid. The drug has been well tolerated, although the high doses present a problem for the veins and a bigger one for the pockets of the patient!