Recent reports have described the occurrence of the nephrotic syndrome in newborn infants.1-4,15,16 This condition has been called "congenital nephrosis," and seems to represent a clinically distinct entity, with a striking familial incidence. The microscopic changes in the disease have been well described. 1-3,15,16 These changes include abnormalities in the renal tubules, alteration of the glomerular epithelial foot processes as seen with electron microscopy, and, in some cases, glomerular basement membrane thickening and glomerular destruction.Two siblings have been studied by us, who clinically showed the typical features of this syndrome. They demonstrate an unusual microscopic feature which has not been stressed in previous reports. In both children, the small renal arteries and arterioles showed marked muscular hypertrophy without fibrinoid change. This change was apparent even when taking into consideration the fact that these vessels are normally prominent in this age group.5 Tubular and glomerular alterations, similar to those pre¬ viously described, were also present, but were less impressive than the vascular changes.Studies were made of the serum and uri¬ nary proteins in one of the patients. Quali¬ tative alterations of the serum protein fractions, and quantitative variations in the renal excretion of the proteins were noted. Clinical Description Case 1.-This infant was the product of an un¬ eventful pregnancy. Spontaneous rupture of mem¬ branes at 35 weeks was followed within 12 hours by normal delivery. The parents were in good health, and are not consanguineous. A 2-year-old brother was in good health.At birth, the patient weighed 2.7 kg., and was said to appear "puffy" and "froglike." Atelectasis was noted, and incubator care with tube feeding was carried out for 5 days. At 10 days of age the baby was discharged weighing 2.45 kg. In spite of "poor feeding," the infant gained about 450 gm. per week, and at the age of 8 weeks was grossly edematous when admitted to the hospital.