This study will evaluate nonhuman primates with surgical as opposed to natural menopause to determine whether hormonal factors affect the immune response or whether the defective immune response of the elderly is due to some other factor. This will be done by, in one case,, bilateral oophorectomy, studying animals with or without replacement hormones. The group of animals with normal menstrual cycles and those given hormonal replacement will be challenged with two strains of E. coli, one a nephropathogenic P-fimbriated form and the other a type 1 fimbriated non-pathogenic organism. The course of the bladder infections in the normal animals, those with surgical menopause and those with replacement hormone therapy will be evaluated and the immune system will also be evaluated prior to and after bladder infections. These animals should determine whether a lack of hormones itself affects the immune response . If so, the type of replacement therapy to reverse this change will have been demonstrated. Studies in elderly postmenopausal monkeys then will be done to determine whether the ideal hormonal replacement reverses the immune defects of the elderly. The knowledge thus gained may have a direct effect on the very high incidence of urinary tract infection in elderly females if it is shown that hormonal replacement therapy is beneficial.