The management of chronic infections of the urinary tract continues to be one of the vexing problems of contemporary infectious disease. The several reasons for the failure to achieve more satisfactory results in spite of the use of the available antibacterial agents have been summarized elsewhere.1-3 Among the reasons for failure of treatment have been listed such factors as (a) the ineffectiveness of the drug used, (b) the action of substances that interfere with the antibacterial activities of the drug used, (c) the failure of the drug to achieve eradication of the organism even though the organisms are sensitive to the drug by the usual testing circumstances, either because the organisms are not multiplying or because they are sequestered in the lesions and unavailable to the action of the drug, (d) the presence of mixed infections leading to the emergence after treatment of a previously suppressed strain of organism,