Rhesus monkeys delivered by cesarean section were asphyxiated under controlled environmental conditions and then resuscitated by positive pressure ventilation with oxygen. In one half of the monkeys an infusion of Tris and glucose was given into the umbilical vein during resuscitation to restore the arterial pH rapidly to normal values. This reduced the time required to establish spontaneous breathing and increased the initial oxygen uptake. There was a linear relationship between duration of asphyxia and the return of respiratory function: for each minute after the last gasp that resuscitation was deferred, subsequent onset of gasping was delayed about 2 minutes and spontaneous breathing about 4 minutes. Nearly one half of the asphyxiated animals developed respiratory difficulties similar to those seen in human infants suffering from the respiratory distress syndrome.