SUMMARY Oxygen consumption was measured in 9 short-gestation infants before feeding and for an hour after, using a closed-circuit metabolism chamber. Using the same system, 02 consumption of 9 term infants was measured for varying periods, beginning one hour from the end of the last feed. In the short-gestation infants a rise was found in the 15-45 minutes after feeding; 02 consumption then fell, and after 60 minutes had reached prefeed levels. The term infants showed no decrease with time after the first hour, as would be expected if the effect of feeding on OS consumption extended beyond this. It is concluded that increased O°demand after appropriate feeding does not extend beyond one hour postprandially.The first quantitative description of the effect of feeding on oxygen consumption (VO2) was reported by Lavoisier (1789). He found that, in a temperature of 320C, V02 of an adult rose about 50 % above the resting value during digestion. Bidder and Schmidt (1877) attributed this rise to the 'work of digestion'. This concept of increased intestinal work was challenged by Benidict and Emmes (1912), who showed that V02 rose equally in response to either intravenous or oral amino-acids. A succinct summary of the various theories of the cause of this rise was written by Kleiber (1961). Rubner (1902) introduced the term 'spezifischdynamische Wirkung', which possibly by mistranslation has become specific dynamic action (SDA).Early measurements of SDA in infants were made by Rubner and Heubner in 1899. Unfortunately, they compared the metabolic rate of a healthy 71-month-old girl with that of a malnourished boy of 31 months, being then unaware of the effect of age and state of nutrition on basal metabolism. Techniques of measurement have now improved and Murlin et al. (1925) reported that the SDA of ordinary 'feedings' within the first 8 days of life was small, the largest increase being 12 % after a feed of 12 % lactose. Since then a variety of workers using different foods and in differing environments have reported increases from 6 % (Levine et al., 1927) to 32% (Gamalero and Crosato, 1958). Mestyan et al. (1969) investigated the magnitude and thermoregulatory significance of the response to feeding in