Plasma growth hormone-binding protein (GH-BP) activity and the levels of IGF-I and its binding proteins (IGFBP) were studied in eight girls with Turner's syndrome before and during recombinant-hGH (r-hGH) administration. Growth hormone and GH-BP activity were assayed at baseline and hourly, over a 12-h period, after an intramuscular bolus of 0.09 mg/kg of the hormone. After 7 d, each patient received r-hGH at 0.33 mg/kg/weekly s.c. every day at nighttime; plasma growth hormone-binding protein activity, blood IGF-I, and IGFBP were evaluated before and on d 7, 30, 180, and 360. Baseline reference values were obtained from 10 bone age-matched healthy girls. Basal GH-BP activity, IGF-I, and IGFBP levels were similar in patients and controls. Four h after the intramuscular injection, GH-BP activity maximally increased and returned to baseline 6-7 h later; during long-term r-hGH administration GH-BP activity peaked at +180 d but declined to pretreatment at +360 d. IGF-I, IGFBP-3, and IGFBP-4 increased under r-hGH and, in contrast to GH-BP activity, remained high throughout the study. In conclusion, in girls with Turner's syndrome, GH-BP activity, IGF-I, IGFBP-3, and IGFBP-4 are induced by r-hGH. However, the increase of IGF-I and IGFBP-3 does not require an increased level of the cellular growth hormone receptors, as suggested by the unchanged +360 d values of plasma GH-BP activity compared with baseline.(ABSTRACT TRUNCATED AT 250 WORDS)