Adipose tissue blood flow (ATBF) was examined in rat parametrial fat by the 133-Xe elimination method. Intravenous infusion of glucose to fed rats resulting in blood glucose concentrations of 10-12 mmol X 1(-1) caused a significant reduction in ATBF (-37%). Similar infusions to 48 hour fasted rats had no consistant effect on ATBF. Glucose infusion caused a significant rise in plasma insulin concentrations in both fed and fasted animals, although the average concentration in fasted rats given glucose did not exceed the control value in fed animals. Insulin added to the glucose infusion caused a similar reduction in ATBF in fasted animals as that seen after glucose alone in fed animals (-38%). Guinea pig anti insulin serum administered intravenously to fed rats elicited an increase in blood glucose concentrations similar to that seen after glucose infusion, but was without effect on ATBF. These results suggest that the effect of glucose on ATBF is secondary to a release of insulin resulting in plasma levels above those found in fed control rats. Infusion of nicotinic acid also reduced ATBF without influencing blood glucose concentration and in spite of insulin concentrations lower than in fed control rats. Since both insulin and nicotinic acid inhibit the formation of c-AMP in adipocytes, it is hypothesized that both compounds decrease ATBF by decreasing the release of the vasodilator adenosine from the cells.