Detailed clinical observations were made on the respiratory behavior of 96 newborn infants, 69 of whom were prematurely born. It was found that the infants could be divided into 3 main groups depending on the trend taken by their respiratory rates during the first few hours following birth. All of the severe respiratory insufficiency and all the deaths occurred in the group of infants whose respiratory rates were approximately normal during the first hour but subsequently increased to 60 or more per minute sometime during the next 2 days. Some of the latter infants died during this 48-hour period of initial respiratory distress; others appeared to recover and some of these died a few days later. There was a greater tendency for infants whose birth weights were 1500 gm. or less to have an increase in their respiratory rates during the first day or two following birth than for infants who weighed more than 1500 gm. at birth. The trend of the respiratory rate was helpful in planning oxygen therapy during the first 2 days. Satisfactory criteria for using oxygen therapy after the first 2 days were not developed from the data in this study. Retraction of the chest wall on inspiration during the first 24 hours was minimal or absent in infants whose respiratory rates did not increase after the first hour.