Twelve postmenopausal women who experienced frequent urinary tract infections were found to have atrophic vaginitis. Four of them who were taking sulfonamide preparations chronically also had an interstitial nephritis manifest by decreasing glomerular filtration rate and eosinophiluria. Treatment consisted of a Betadine douche daily for 1 week, administration of an appropriate nonsulfonamide antibiotic, and institution of estrogen therapy to restore glycogen deposition in the vaginal epithelium and promote return of a normal vaginal pH and bacterial flora. Prior to estrogen therapy, the frequency of infection was four per patient per year. During a follow-up observation period ranging from 2 to 8 years, there have been only four infections in the entire group. When sulfonamides were discontinued in the 4 patients with manifestations of interstitial nephritis, the eosinophiluria cleared, and the glomerular filtration rate increased significantly.