SummaryUsing the power ponderosity index of Benn, weigh (W)/height (H)p, (W/Hp) where the value ofpis determined so that the correlation of height andW/Hpis zero, a set ofpvalues was obtained from longitudinal data of 630 healthy, white, middle class children ranging in ages from birth to 9 years. Our data revealed two turning points in the relative velocity of change of height and weight not previously recognized by separate studies of velocity changes in weight and height related to chronological age. The value ofpincreased from birth (1.72) until about 1 month (2.39) for girls, and 5 months for boys (2.30), the first turning point, and then fell to a nadir at age 18-21 months for girls (1.75) and 21-24 months for boys (1.73), the second turning point. This fall to the nadir represents the greater influence of velocity change in height over weight. From then to age 9 years, there was a gradual and steady increase inp, greater for girls than for boys, representing the greater influence of velocity change in weight over height. The values ofphave now been estimated for white, middle class children over the ages of birth to 9 years and may have utility in studies which compare obesity indicators.