In the past, several laboratory tests, which have included selective straining of the urinary sediment, and observation of the sediment after intravenous administration of bacterial pyrogen or adrenal corticosteroid have been employed in an attempt to distinguish between upper and lower urinary tract infection. In addition, as mentioned in the present report, measurements of O-specific hemagglutinating and other antibody titers, tests of maximal concentrating ability and determination of activity of certain enzymes in the urine have also been proposed as methods for differentiating renal involvement in recurrent bacteriuria. Moreover, in women, the pattern of recurrence, i.e., relapse versus reinfection, has been employed as an indication of the site of infection in women with asymptomatic infection. Although these procedures all may be helpful in characterizing groups of patients, none is specific in individual patients, and to date only bilateral ureteral catheterization has been shown to localize infection with relative certainty. However, ureteral catheterization cannot be justified for the routine evaluation of patients with recurrent bacteriuria. For the time being, it is my feeling that these studies should be reserved primarily as clinical research tools and not be applied routinely in the management of women with recurrent bacteriuria. It is anticipated that the greater availability of typing sera, coupled with a clearer definition and description of population groups studied, eventually will lead to a rational approach to these infections.