The aim of these studies was to determine if meal requests and changes in hunger ratings in humans were related to spontaneous changes in blood glucose concentration. In our first study, 18 healthy subjects were acutely isolated from food ant time cues. Blood glucose was continuously monitored online and visual analog ratings of hunger were obtained following an overnight fast. Spoken meal requests, if they occurred, were also recorded. In 83% of the subjects, both the perception and behavioral expression of hunger, as assessed by changes in hunger ratings and meal requests, were preceded by, and correlated with, brief, transient declines in blood glucose (nadir: -10% at 27 min). The pattern, magnitude and time course of these declines was similar to those observed in rats. This significant association, between increased expression of hunger and declines in blood glucose, is being tested in a second, ongoing study using acute insulin infusions to mimic spontaneous transient declines in blood glucose. Each subject was studied twice: either insulin or saline was infused while hunger ratings were obtained. Preliminary results in five subjects indicate that hunger ratings increased after insulin-induced transient declines in blood glucose. No change in hunger ratings occurred when blood glucose concentration was stable. These results suggest that this temporal pattern of blood glucose reflects an antecedent physiological event or provides a signal related to the expression of hunger in humans. Further understanding of human eating may result from investigation of the complex interaction of physiological and other factors in an experimental setting that allows the expression the behavior under study.