Effects of weaning age on blood glucose, ketones, and nonesterifid fatty acids were examined using 16 Holstein heifer calves. Animals entered the study at 6 f 3.5 d of age and were fed 1.8 kg of milk twice daily to 28 (early weaning) or 56 d (late weaning) and a commercial pelleted calf starter from 0 (early) or 28 d (late). Blood was sampled once weekly for 14 wk and analyzed for p-hydroxybutyrate and acetoacetate. Plasma was analyzed for glucose and nonesterifid fatty acids. Blood phydroxybutyrate increased with increasing grain intake and was greater during wk 0 to 4 and 5 to 8 in late. Blood acetoacetate followed trends similar to p-hydroxybutyrate and averaged 23.8 and 16.1 ph4 in calves weaned early and late, respectively. Plasma glucose and nonesterifid fatty acids declined with age and were lower during 5 to 8 wk in calves weaned early. Data suggest that ketone concentrations resulted from alimentary ketogenesis, which increased rapidly after weaning.