The metabolism and action of insulin and glucagon were investigated in goats during mid lactating (50 days postpartum) and during the dry period. The animals were fed hay and concentrate during lactation (1:1) and only hay during dry period. Pulse doses of unlabelled insulin and glucagon were injected intravenously. The disappearance of insulin from the circulation was faster during lactation than during dry period; the metabolic clearance rate of insulin was significantly increased during lactation. In contrast, the kinetic parameters of glucagon disappearance were very similar during the two periods. Basal plasma hormones (i.e. before hormone injection) were higher during lactation than during dry period; the molar ratio insulin:glucagon was left unchanged. The increase in plasma insulin following glucagon-stimulated hyperglycaemia was similar during the two periods. The ability of insulin to elicit a decrease in blood glucose was markedly impaired during lactation when compared to dry period. In contrast the ability of glucagon to increase blood glucose was slightly improved during lactation. Those endocrine changes could be related to the effect of both lactation and diet.