Newborn rabbits were overfed by encouraging them to suckle from two lactating does. Rabbits fed in this way (double fed) were compared with littermate controls (single fed) at age 7,14, and 21 days. The double-fed rabbits gained weight more rapidly and at each age contained a higher percentage of fat than their single-fed counterparts. During the 1st wk the double fed rabbits stored some of their extra fat in the cervical and interscapular adipose lobes. Double-fed rabbits utilized their feeds more efficiently than single fed rabbits in that they gained more weight per unit milk intake and their gross energetic efficiency was 10-20% higher. In a second series of experiments oxygen consumption rate was measured in singleand double-fed rabbits at ages 7,14, 21, and 28 days. The relation between oxygen consumption and body weight were similar. We conclude that rabbits respond to overfeeding with an increased rate of weight gain associated with extra fat deposition, and this is associated with increased energy efficiency.