This study demonstrated the feasibility of utilizing the (3-13C-methyl) caffeine breath test (CBT) in children and adolescents, and examined the effect of gender, age, and puberty on the CBT. The CBT, expressed as the 2-hour accumulative exhalation of labeled CO2 (2-hour CO2), was compared to the CBT results in the adult. The 2-hour CO2 values were higher in the children than the adult, and the decrease in the CO2 values occurred in males during late puberty and in females during early puberty.