The concurrent effects of mid-parent height and tempo of maturation on variation of the individual growth curve were examined. Data of 183 boys from the Wrocław Growth Study were used. The functional and biological parameters were derived from fitting Preece-Baines model 1 to individual data. All subjects were divided into three categories of mid-parent height and maturation rate, resulting in nine groups. MANOVA showed significant differences in the functional and biological parameters for three maturity and mid-parent height groups, separately. However, insignificant interactions indicated independence of the two factors. Univariate analysis revealed that the first factor (tempo of maturation) adjusts time and velocity at the beginning (T1, V1) and peak (T2, V2) of the adolescent growth spurt. This factor accounts for the shape of the curve. It places the curve along age and velocity axes. The other factor (mid-parent height) is responsible for general elevation of the growth curve on the centile distribution, placing it on the appropriate centile. This regulates height parameters, i.e., height at take-off (H1), height at peak height velocity (H2), and adult height (AH). The simultaneous influence of the two factors leads to estimation of a more specific and more probable type of a curve. This kind of the estimation allows diminishing variance and prediction error. Am. J. Hum. Biol. 9:555-563, 1997. © 1997 Wiley-Liss, Inc.