The plasma concentrations of free fatty acids (FFA), glycerol and insulin as well as the blood glucose concentration have been followed in two groups of subjects after infusions of theophyllamine. Each individual was examined twice. The 5 subjects in group 2 were given an infusion of norepinephrine before the theophyllamine at one of the examinations and saline at the other. The 6 subjects in group II were given an infusion of norephinephrine at both examinations, followed by theophyllamine on one occasion and by saline on the other. Thus, the subjects in both groups served as their own controls. It was found that theophyllamine caused lipid mobilization, as measured by the plasma FFA and plasma glycerol concentrations, both when given as the only active drug and when given after norepinephrine. The blood glucose concentration rose slightly after norepinephrine and the plasma insulin level increased concomittantly. When theophylline was given as the only active drug, there was no increase in the blood glucose but the plasma insulin concentration rose slightly.