While the above case does not serve especially well to illustrate a pre-operative diagnosis of renal tuberculosis, inasmuch as there was no X-ray and no T. B. bacilli were ever found in his urine, it does bring out a certain fairly infrequent symptom which would be extremely—I might almost say—fatally, misleading in the diagnosis of surgical conditions of the genito-urinary tract but for other aids in diagnosis. I refer to the phenomenon of crossed renal pain. That this was renal involvement of a kind requiring surgical interference was well evidenced by the blood and pus in his urine, together with his history of pain at various times. But had we gone strictly by the pain, whose location was chiefly in his right testicle and right side, the patient would have been the victim of a nephrotomy, at least of his right kidney. However, the presence of 2.4% urea with a slight amount of pus (probably pus from the bladder as the Luys’ separator does not always preclude this possibility) from the right ureter as against a very slight amount of urea and a large amount of pus from the left ureter, dispelled all question of doubt as to which kidney should be explored. _Case II, E. B._—Male, gave the following history: A father and two brothers died of pulmonary tuberculosis. Others in the family had lived to ripe ages. At the age of 31, the patient passed blood in his urine. Three years later he experienced right renal colics and slight irritability of the bladder. The colics continued every few weeks for seven years. Then, because of an attack of intense bladder symptoms, and profuse hematuria, Dr. Charles McBurney diagnosed the condition as renal calculus (this was in 1900—the pre-radiographic days), explored the kidney, and found nothing. The operation relieved the renal colics. But the bladder still caused him untold agony, the patient urinating blood every two or three hours. On January 16, 1908, eighteen years after the first symptoms of his disease, the patient consulted Dr. Keyes, having in the interval suffered three vain searches for stone and two cystoscopies, and having developed double tubercular epididymitis. Physical examination revealed nothing except ridgy seminal vesicles. The urine was cloudy and contained a small amount of albumin, pus, red blood cells, a few hyaline casts and many T. B. bacilli. The X-ray revealed an irregular shadow in the right kidney region, which the radiographer reported as “consistent with a diagnosis of renal tuberculosis.” Cystoscopy was now tried again, but failed on account of the extreme pain attending it. Recourse was then had to the experimental polyuria test, which showed fairly good, though deficient renal function. The diagnosis of tuberculosis of the right kidney being now fairly certain, the kidney was removed in April, 1909. Though the pelvis was uninvolved, the parenchyma was riddled with abscesses, the latter confirming the diagnosis.