<sup>15</sup>N-nitrogen balances before and on human growth hormone (hGH) were studied in 13 girls with Turner syndrome (TS) aged 4.4–16 (median 13.2) years (45, X0 or equivalent, no X0/XX mosaicism, no estrogen replacement). The results were compared with those reported from 9 patients with growth hormone deficiency (GHD). The TS patients received subcutaneous hGH doses of 2 × 3 (group A, n = 6), 3 × 2 (group B, n = 3), or 2 × 6 (group C, n = 4) IU/m<sup>2</sup> on consecutive days. The mean <sup>15</sup>N dose given to the patients of groups A and C was higher (13.6 mg/kg) than that given to those of group B (2.7 mg/kg). The lower hGH doses in the first two groups induced small positive mean <sup>15</sup>N balance changes (+0.6 ± 0.6 mg/kg <sup>15</sup>N, group A; +0.03 mg/kg, group B). The higher hGH dose in group C caused a more marked mean balance change (+3.0 mg/kg <sup>15</sup>N) comparable to that in GHD patients (+3.2 mg/kg). Individual variation of response, however, was larger in patients with TS than in those with GHD. With low and high hGH doses, there were responders and nonresponders. It is concluded from this pilot study in a small number of cases that <sup>15</sup>N balance studies might be potentially useful to choose the appropriate hGH dose for long-term treatment in TS patients.