The short- and long-term effects of simultaneous administration of terbutaline and betamethasone were investigated in 8 gravidas treated for preterm labor. Their plasma concentrations of glucose, insulin, glucagon, C-peptide, lactate and potassium were compared to a control group receiving intravenous magnesium sulfate and betamethasone. The patients on terbutaline therapy had a marked hyperglycemia at 11 h which remained elevated for 48 h. There was a simultaneous rise in plasma insulin and C-peptide, and a fall in plasma glucagon. Lactate levels were markedly elevated. Only 1 of the 8 patients had an abnormal glucose tolerance test at 1 week of therapy. The metabolic changes of control patients were minimal in comparison and there was no lacticacidemia. This suggests that glucocorticoids potentiate the hyperglycemic response of terbutaline.