The severest case of acute pyelitis of pregnancy that ever came under our observation was one in which the patient was in the fifth month of her first pregnancy. She was taken seriously ill, with a temperature of 103.4 F. The urine from the right kidney showed 2,560,000 pus cells and from the left kidney, 2,880 pus cells per cubic millimeter, and the cultures showedB. coli.There was marked prostration, icterus, and acute dilatation of the heart. The ureteropyelograms showed enormous dilatation of both kidney pelves and ureters, with extreme torsion and kinking, and marked outward displacement of both ureters. GROUP 1. ACUTE PYELITIS In a study of eleven subsequent cases of acute pyelitis, there was marked dilatation of both ureters and kidney pelves in six cases. In two cases only one side was injected, in both of which cases the injected side was found dilated. In three cases