This is a report of measurement of gastric acidity in the prematurely born baby during the first 10 days of life. The studies heretofore reported have been in newly born full-term infants. It has been established that nearly all full-term babies secrete gastric acid within three to six hours of birth. Indeed the majority of investigators (Hess, 1913; Griswald et al., 1925; Chievitz, 1922)1-3 do not believe that congenital achlorhydria exists, and, in fact, they believe that free hydrochloric acid is always present in the gastric juice of the unfed infant at birth. However, Strauss and Castle (1932)4 and Miller ( 1941 )5 found achlorhydria in the newly born infants, but only in those babies whose mothers were achlorhydric. Miller (1941)5 further reported that free acid varied directly with the birth weight; i.e., the lower the birth weight, the lower the gastric acidity, and that there was no