Obesity (Ob) and type 1 diabetes (T1DM) are associated with increased inflammation and oxidative stress, which are major pathogenetic pathways toward higher cardiovascular risks. While long-term exercise protects against systemic inflammation and oxidation, acute exercise actually exerts pro-inflammatory and oxidative effects, prompting the necessity for better defining these molecular processes in at-risk patients; in particular, very little is known regarding obese and T1DM children. We therefore examined key inflammatory and oxidative stress variables during exercise in 138 peripubertal children (47 Ob, 12.7±0.4 yr, 22F, BMI% 97.6±0.2; 49 T1DM, 13.9±0.2 yr, 20F, BMI% 63.0±3.6; 42 healthy, CL, 13.5±0.5 yr, 24F, BMI% 57.0±3.6), who performed 10 bouts of 2-min cycling ~80% VO2max, separated by 1-min rest intervals. Blood samples were drawn at baseline and peak-exercise. Ob displayed elevated baseline interleukin-6 (IL-6, 2.1±0.2 pg/mL, p