INTRODUCTION: Acylation-stimulating protein (ASP) is an adipocyte-derived protein that contributes to fatty acid clearance. Regular exercise training improves fatty acid handling. OBJECTIVE: To examine the effect of acute exercise and short-term endurance training on ASP levels. SUBJECTS: Eight untrained men (age: 23.5+/-3.4 y; maximal power output (Wmax): 3.7+/-0.6 W/kg body weight). DESIGN: Subjects were trained for 2 weeks. Before and after training, blood was sampled during a 3-h exercise test, and insulin sensitivity was assessed by an insulin tolerance test. RESULTS: Before training, ASP levels decreased during exercise (from 17.9+/-2.9 to 15.5+/-3.7 nmol/l at t=0 vs 180, P<0.05). Endurance training decreased fasting ASP levels significantly (17.9+/-2.9 vs 13.4+/-2.3 nmol/l pre- and post-training, P<0.001). Interestingly, after 2 weeks of endurance training, ASP levels tended to increase during exercise (from 13.4+/-2.3 to 17.2+/-4.5 nmol/l at t=0 vs 180, P=0.09). Baseline ASP levels correlated negatively with insulin sensitivity both before (r=-0.86, P<0.01) and after training (r=-0.82, P<0.05). CONCLUSION: Short-term endurance training reduces baseline ASP levels. These data fit with the hypothesis that reduced ASP levels indicate improved ASP sensitivity.