The purpose of the present study was to test the hypothesis that exercise-induced increase in IGFBP-1 is not always linked to a decrease in blood glucose level and to examine if the decreasing levels of liver glycogen during exercise may be associated with the increase in IGFBP-1. Three groups of rats were submitted to a 70-min treadmill exercise. One group of rats were normally fed and the two others had their food intake restricted by 50% (1/2 fast) the night before the experiment. One of these two 1/2 fasted groups of rats were infused (iv) with glucose throughout exercise to maintain euglycemia. Exercise in non-infused 1/2 fasted rats, compared to the normally fed rats, resulted in significant lower blood glucose (min 70) and insulin levels, and liver glycogen content, no change in IGF-I, and significant higher increases in FFA, glycerol, ß-hydroxybutyrate, and IGFBP-1. Maintenance of euglycemia during exercise in glucose-infused 1/2 fasted rats reduced to a large extent the decrease in insulin levels but only slightly attenuated the lipid response and the IGFBP-1 response seen in non-infused 1/2 fasted rats. Comparisons of all individual liver glycogen and IGFBP-1 values revealed that liver glycogen values were highly (P < 0.001) predictive of IGFBP-1 response during exercise (R = 0.564 ). The present results indicate that IGFBP-1 response during exercise is not always linked to a decrease in plasma glucose and suggest that the increase in IGFBP-1 during exercise may be related to the decrease in liver glycogen content.