Six young obese females (20.5±1.22 years; BMI=34.5±4.3 kg/m2) participated in a resistance exercise (RE) protocol (12 exercises, 4 sets × 15 repetitions at 60% of 1RM), an aerobic exercise (AE) protocol (3 sets × 10 min ergometer cycling at 60% of maximal heart rate with 5 min of rest between sets), and a control session. Blood samples were collected before, and immediately after and 10 h after exercise. All protocols were done in follicular phase of the menstrual cycle. ANOVA (3×3) with repeated measure on exercise (3 levels) and time (3 levels) factors was used to determine the effects of exercise protocol, time and exercise protocol by blood sampling time interaction, triglycerides, HDL-cholesterol, LDL-cholesterol, and glucose concentrations. Immediately and 10 h after AE, serum leptin was significantly lower (p <0.05). Serum insulin after AE was lower than after RE and control sessions (p <0.05). Furthermore, no significant differences were found in serum leptin and insulin between RE and control sessions immediately after and 10 h after exercise. Blood glucose, triglycerides, total cholesterol, HDL-cholesterol and LDL-cholesterol were unchanged in both exercise protocols. In conclusion, AE resulted in a serum leptin reduction and suppressed the circadian rhythm of serum insulin when sampled immediately and 10 h after exercise; instread, RE did not result in serum leptin or insulin changes. © Springer-Verlag Italia 2008.