To the Editor:— I read with great interest the case of a 32-year-old woman with chronic urinary-tract infection ( 194 :1396, 1965). I do not agree with the comments of E. H. Kass, MD, on this case. Before a final diagnosis is made, acid-fast infection of the kidneys should be considered by culture of 24-hour urine specimens for acid-fast bacilli, guinea-pig inoculation, and administration of a tuberculin patch test. Staphylococcus and Proteus in the urine may indicate secondary infection in tuberculosis. When acid-fast infection is eliminated, these bacteria may be considered the true pathogens. The magic number of 100,000 bacteria per milliliter indicating infection and anything under this count being contamination is arbitrary and dangerous. In most chronic infections, very few bacteria or pathogens occur in the lesions, and frequently the cultures are completely sterile or negative. In the past, we considered six cultures satisfactory, but presently we take ten cultures