This paper is concerned with favourable levels of constitutional cardio-vascular health indicators during childhood and adolescence. A cross-sectional randomised sample of healthy Czechoslovakian children was investigated, because this population is habituated to a favourable life style. Twenty girls and 20 boys at ages 8, 12 and 16 years were recruited to the study. Statistical data for means and standard deviations are presented with regard to maximal aerobic power, haemodynamic variables such as arterial blood pressure, heart rate at submaximal and maximal muscular exercise, body fat content, blood lipids including total cholesterol and its fractions, high- and low-density lipo-proteins, fasting triglycerides and the apo-lipo-protein profile. The maximal oxygen uptake in absolute values increased with age in both sexes and the boys appeared to average higher than the girls at each age. When maximal aerobic power was expressed on a total body weight basis, boys appeared to average higher at age 16 years (56 ml X min-1 X kg-1) than girls (45.8 ml X min-1 X kg-1). The highest recorded heart rate for ergometric work averaged close to 200 min-1 in both sexes with no significant age differences. The diastolic blood pressure at rest did not change significantly with age or sex. Serum cholesterol levels were found to decrease significantly after puberty in boys (post-pubertal dip), but in the girls there was found no systematic change in mean values with age. When HDL was expressed as a percentage of total cholesterol there appeared to be no differences related to age and sex.(ABSTRACT TRUNCATED AT 250 WORDS)