Growth before and during treatment with biosynthetic human growth hormone (hGH) was studied in 13 patients with Turner syndrome (TS) and a growth hormone (GH) response of less than 10 micrograms/l to two standard provocative tests. During 1 year of treatment with hGH (0.15 IU/kg per day) height velocity (mean +/- SD) increased significantly (P less than 0.001) from 3.7 +/- 1.8 cm/year to 7.6 +/- 1.5 cm/year. The auxological data in these girls before and during treatment with hGH were similar to those observed in TS patients with a normal response of GH to pharmacological stimuli. It is concluded that in girls with Turner syndrome GH testing should only be performed when height velocity is below the Turner norm. In TS patients with residual growth potential a clinically significant growth acceleration can be obtained with a higher-than-replacement dose of hGH, i.e. 0.15 IU/kg per day, regardless of GH testing.