Heart rate, systolic and diastolic blood pressure and electrocardiographic changes were studied in 80 healthy children during treadmill exercise with Bruce protocol. Mean duration of exercise in boys increased from 10.01 +/- 1.61 minutes at age four to six years with a mean body surface area of 0.75 +/- 0.06 m2, to 17.86 +/- 2.66 minutes at age 13 to 15 years with a mean body surface area of 1.48 +/- 0.10 m2. Mean endurance time in girls increased from 11.06 +/- 1.92 minutes at age four to six years with a mean body surface area of 0.76 +/- 0.08 m2, to 15.69 +/- 2.23 minutes at age 13 to 15 years with a mean body surface area of 1.41 +/- 0.07 m2. Mean maximal heart rate was 193.38 +/- 10.89 beats/minute in boys and 196.78 +/- 10.99 beats/minute in girls. The maximum level of systolic blood pressure attained at peak exercise was lower in girls. Although data of healthy Turkish children including mean endurance time, heart rate and blood pressure responses to exercise were consistent with the results from several countries using the Bruce protocol, mean maximal heart rates for all groups were slightly higher than those obtained with the Balke protocol. The data obtained from this study offers age- and size-appropriate normal data in both sexes in healthy Turkish children and may be used as reference values during treadmill exercise.