Relationships among anthropometric indices of growth and creatinine and hydroxyproline excretion were studied over a 2-year longitudinal period in 124 preadolescent girls. Four groups of girls were selected: low-income white (LIW), middle-income white (MIW), low-income black (LIB) and middle-income black (MIB). Changes in body height, weight, subcapsular skinfold, bone density of the phalanx and bone mineral of the radius and ulna were used as indices of growth in relation to creatinine and hydroxyproline excretion. There were no significant differences in subcapsular skinfold among the groups. Bone density of the phalanx and bone mineral of the radius and ulna were significantly greater in blacks than whites at each age. Mean values for urinary creatinine concentration ranged from 0.115 to 0.209 g/dl from 9 to 11 years of age and tended to be greater for the middle-income than the low-income girls. Urinary hydroxyproline (g)/creatinine (g) ranged from 0.072 at 9 to 0.128 at 11 years of age with no significant differences between groups. All measurements showed significant increases with age. Significant positive correlations were seen among several indices in both racial groups and are discussed. INDEX WORDS: Growth, height/weight, hydroxyproline/creatinine excretion, race-income groups, subscapular skinfold, bone density, bone mineral content, preadolescent girls.