Recently, a most unusual and at first perplexing intrathoracic condition was discovered in a new-born infant, which we considered of sufficient rarity and interest to justify reporting.REPORT OF CASE B., a boy, was born Oct. 2, 1924, weighing 3,250 Gm. The delivery was entirely normal and respiration started promptly and the baby appeared to be perfectly well until the fourth day after birth. At this time he suddenly became quite cyanotic and had great difficulty with respiration. One grain of caffein sodium benzoate was administered by hypodermic injection and oxygen inhalations were given, following which the condition of the baby distinctly improved. In addition, 30 cc. of citrated blood was injected subcutaneously. A short time later, an examination of the baby revealed that the right side of the thorax failed to expand on inspiration. The percussion note was dull over the entire right side of the chest, and the breath sounds in this area were barely audible. No r\l=a^\leswere heard. A diagnosis of hydrothorax was made, the etiology of which was perplexing, particularly since the baby had a normal rectal temperature (98.6 F.) and also since the onset of symptoms had occurred very suddenly. A roent¬ genogram of the chest was taken, which revealed an extensive accumulation of fluid in the right pleural sac. The chest was aspirated, and 110 cc. of fluid was removed, which resembled egg yolk in color. On examination, the aspirated fluid was found to be entirely devoid of cells, leukocytes and bacteria, and proved to be sterile on culture. Following the removal of this fluid, the difficulty in res¬ piration disappeared for a few hours. The following day, however, a recurrence of respiratory embarrassment necessitated aspiration again, and 150 cc. of yellowish fluid was removed, which microscopically resembled that removed the day previous. The fluid was stained with sudan III, and was found to contain innumerable fat droplets taking a bright red stain. In addition, a test for bile was negative. It now became evident that we were dealing with a case of chylothorax, due possibly to rupture of the thoracic duct. The golden yellow color of the chylous fluid apparently was derived from the pigment (lactochrome) present in the colostrum the baby obtained at the breast, although no attempt was made to identify this pig¬ ment aside from excluding the presence of bile in the intrathoracic fluid.The chest was aspirated the third time on October 11, and daily thereafter until October 22, on which date the baby died, weighing 2,955 Gm. On October 11, nine days after birth, the aspirated fluid was distinctly less yellow than on previous dates, and became milky white the following day. At this time, when the baby was 10 days of age, 3 minims of sudan III were given with each feeding. The following five days 0.5, 1, 2, 2.5 and 3 cc. respectively, of this dye