Carbenicillin indanyl sodium (orally, 500 mg every six hours for 7 to 23 days) was evaluated in 16 episodes of bacteriuria. Pseudomonas aeruginosa, Escherichia coli, and multiple bacteria caused ten, three, and three infections, respectively. During therapy, serial urine cultures were negative for initial infecting organisms in 15 of 16 cases. Eight of ten patients had prompt resolution of symptoms, including five of six with infections due to Pseudomonas organisms alone. Initial bacteriologic cures were obtained in all ten patients with either symptomatic or asymptomatic infections due to Pseudomonas alone but relapses occurred in two. Serial urine cultures showed resistant E coli, Klebsiella, and multiple bacteria in three, five, and one instance, respectively. Four of 14 cases (29%) with adequate follow-up had sterile urine on final follow-up culture. Carbenicillin orally is useful for therapy of Pseudomonas bacteriuria and other urinary tract infections of mild to moderate severity, but relapses may occur. In addition, superinfection or reinfection with resistant organisms, particularly Klebsiella, may be observed.