Circulating concentrations of adiponectin, an adipocyte-derived protein, are increased by thiazolidinediones and by weight reduction, accompanied with improvement in insulin sensitivity. The effect of exercise training, another therapy to increase insulin sensitivity (SI), on adiponectinemia is currently unclear. The present study was undertaken to clarify whether exercise training-induced increase in SI is related to changes in adiponectinemia in healthy men. Twelve healthy non-obese men underwent ergometer training at lactate threshold (LT) intensity for 60 min/day for 5 days/week for 6 weeks. An insulin-modified intravenous glucose tolerance test was performed before and at 16 h and 1 week after the last training session to determine SI using a minimal-model approach. Serum levels of adiponectin were determined at the same time. After the exercise training, Vo₂max and LT were significantly increased by 7.2% and 22.3% (P<0.01), while BMI and body fat mass remained unchanged. SI was significantly increased at 16 h after the last training session (from 7.0 ± 3.1 to 9.6 ± 3.6 [×10^-4·(μU/ml)^-1·min^-1], P<0.01), but returned toward the basal levels at 1 week after the cessation of the training. Serum adiponectin concentrations before the training (20.9 ± 7.4 μg/ml) were positively correlated with SI. The concentrations were slightly but significantly decreased at 16 h (17.2 ± 6.6 μg/ml, P<0.05), and returned to the basal values at 1 week after the training. From these results, it can be concluded that exercise training-induced increase in SI is not dependent on the increase in adiponectinemia in healthy men.