Two experiments utilizing Holstein cows (second or later lactations) were conducted to better understand hormonal regulation of carbohydrate, lipid, and protein metabolism in early postpartum cows with special emphasis on ketotic cows. Blood was sampled hourly for 24 hours in the first experiment and for 12 hours in the second experiment, at 2 weeks prepartum, at 3 weeks postpartum, during a feed-restriction (50%) induced ketonemia (at approximately 6 weeks postpartum), and after a 4 week recovery period. Cows were fed alfalfa hay prepartum, and a complete mixed diet postpartum.;Onset of lactation in the first experiment and feed restriction to induce ketonemia in both experiments caused mean plasma concentrations of acetoacetate, beta-hydroxybutyrate, free fatty acids (FFA), and growth hormone (GH) to increase and glucose and insulin to decrease. Concentrations of total amino acids (TAA) and glucagon were increased at 3 weeks postpartum and were decreased to equal prepartum concentrations during the ketonemic period in the first experiment. Glucagon concentration tended to be decreased in the ketonemic period during the second experiment. Resumption of ad libitum feeding caused most metabolites and hormones to return to prepartum concentrations. Feeding responses were most evident for FFA, TAA, and GH, and were most dramatic during the ketonemic and early lactation periods. FFA and TAA concentrations decreased after feeding, whereas GH concentration increased after feeding. The metabolite and hormone changes from period to period and after feeding within periods represent adaptations of cows to provide energy and protein substrates to sustain life and milk production.;Bovine glucagon (520 (+OR-) 20 ug) was injected into each cow during each period in the second experiment to measure parameters of glucagon kinetics. Distribution space, turnover rate, and metabolic clearance rate were not different between periods. Pre-injection glucagon concentration was significantly decreased in cows during the ketonemic period. Secretion rate of glucagon was decreased (P < .10) in ketonemic cows. Injection of glucagon caused equal incremental increases of glucose, FFA, and insulin concentrations in all periods. Ketonemic cows seem to have equal gluconeogenic capacity as normal cows when stimulated with exogenous glucagon, therefore lactation ketosis may be caused by decreased secretion of glucagon.