SUMMARYFor 6 months details of every patient who had his or her urine sent to a laboratory for bacteriological examination and the result of such examination were entered on a computer-card. A total of 15,606 cards were completed with information in code recording the sex and age of a patient, the origin of the request, the presence or absence in the urine of an excess of protein or cells, the culture result and the name of any significant organism isolated together with its sensitivity to various antimicrobial drugs. This information was interrelated in a computer, and in some cases the resulting numerical details were expressed as rates so as to eliminate the effect of uneven sex and age distribution. In this waythe occurrence ofurinary tract infection and the type of infecting organism in persons of either sex at various ages was examined according to whether the patient was in hospital or general practice. The sensitivity pattern of each type of significant organism isolated was established according to its source. The association between patients of either sex and various ages who had, or did not have, bacteriologically evident infections and the presence in their urine of an inflammatory exudate was investigated. Finally, the capacity of each type of infecting organism to produce such an exudate was estimated.It was shown that hospital and general practice experience of urinary tract infections differed widely, with regard both to the age and sex distribution of those suffering from it, and to the causative organisms concerned and their sensitivities to antimicrobial drugs. It is suggested that these differences were so great that conclusions drawn from any study of this subject conducted in one of the two areas cannot be applied to the other, and that those derived from a mixture of the two will vary according to the relative sizes of each of the components.