Measurement of PBI values in healthy pre-adolescent Negro school children (N = 437) revealed a mean value of 6.4 ±.06 mg/100 ml while in a similar population of Caucasian children (N = 614) a normal mean value of 5.6 ±.07 mg/100 ml was observed. The difference had a P value <.001. Comparison of 131I T3 red cell uptake values in these two groups demonstrated a significant depression (P <.01) in the Negro children. TBG saturation capacities of Caucasian children were 24.7 ± 0.6 (S.E.M.) for ages 6 to 11 years and 21.3 ± 1.1 for ages 12 to 19 years which were not different from the adult values of 22.9 ± 0.8. In Negro children these values were 28.9 ± 0.7 for ages 6 to 11 and 25.4 ± 1.9 for ages 12 to 19 which were significantly different from their Caucasian counterparts. Adult Negro PBI values of 5.6 ± 0.25 and TBG of 24.5 ± 1.5 were not different from adult Caucasian values. Thyroxine-binding pre-albumin (TBPA) saturation capacities were significantly depressed in pre-adolescents (Caucasian 71 ± 7; Negro 69 ± 4) and adolescents (Caucasian 105 ± 13; Negro 109 ± 19) below the normal adult values but no racial difference was displayed. It is now apparent that racial origin must be a consideration in the evaluation of pre-adolescent and adolescent PBI and 131I T3 red cell uptake results and that TBPA and TBG capacities may normally alter during puberty in a manner independent of each other rather than reciprocally as has been recently proposed.