(Gln4)-neurotensin, 18 pmolXkg-1Xmin-1, was infused i.v. during 20 min in 10 healthy male volunteers. Adipose tissue blood flow was continuously monitored by measuring the disappearance rate of 99mTc-pertechnetate injected s.c. on the abdomen and thigh. Heart rate and blood pressure were measured and calf blood flow studied by venous occlusion plethysmography. Neurotensin-like immunoreactivity (NTLI) in serum was determined. Infusion of isotonic saline served as control. During intravenous infusion of (Gln4)-neurotensin the first order rate constants of 99mTc-pertechnetate from the abdomen decreased by 21.9 +/- 5.9% from a basal value of 8.3 +/- 0.5% min-1 (p less than 0.01). The reduction in blood flow started after a latent period of 5-10 min and persisted throughout the thirty minute observation period following infusion. A significant correlation (r=0.87, p less than 0.001) was found between the percentage decrease in blood flow from abdominal fat and the body fat content of the subjects as determined from the sum of four skinfolds. Blood flow from thigh fat did not change significantly, nor did heart rate, blood pressure or calf blood flow. During infusion of (Gln4)-neurotensin plasma neurotensin-like immunoreactivity (NTLI) increased successively. Ten minutes after starting the infusion the mean plasma NTLI level had increased from 20 +/- 5 pM to 302 +/- 31 pM; at 20 min it was 473 +/- 51 pM. These concentrations are within the range found after eating a fatty meal. The results indicate that neurotensin plays a physiological role in the regulation of human adipose tissue blood flow and may be of importance for the postprandial uptake of substrates in adipose tissue in certain regions. We suggest that neurotensin deserves consideration as an endocrine hormone affecting the regional deposition of fat postprandially.