Carbohydrate, lipid, hepatic, and thyroid metabolic tests have been carried out on 100 obese subjects. Fifty-eight showed abnormal oral glucose tolerance. Intravenous tolbutamide tolerance was normal in 17 of these, indicating an hepatic cause for their hyperglycemia. Hypercholesterolemia was present in 37 patients, whereas the free fatty acids were elevated in 70. The triglycerides were usually normal. Liver function studies, particularly sulfobromophthalein (Bromsulphalein) excretion, frequently yielded abnormal results. Thyroid tests were normal in most cases. The photomotogram, however, was in the hypometabolic range in 28 subjects. This was associated with a decreased lipidmobilizing response to epinephrine in four of eight patients studied. Weight reduction was accompanied by improvement in all of these parameters. Sodium liothyronine (triiodothyronine) treatment, unlike that of amphetamine phosphate, caused a reversion of a prolonged Achilles reflex to normal.