Intravenous glucose tolerance was measured in manic-melancholic patients given one daily lithium-dose for relapse prevention. It was found that glucose tolerance was increased for some hours after each lithium administration. In the first week of treatment glucose disposal rate was increased up to 12 h after lithium ingestion. In long-term treated patients glucose tolerance was increased 2 h after administration but not 12 h after. Fasting glucose was increased 2 h after lithium administration in long-term treated patients. Concomitant changes in lactate triglycerides, free-glycerol and electrolytes were measured in serum.