We investigated in Turner's syndrome patients whether the decrease in growth hormone (GH) secretion is frequent or sporadic, whether or not reduced GH secretion contributes to insufficient growth, and whether age, spontaneous presence of telarche and/or pubarche, karyotype and weight influence GH secretion decrease. We evaluated GH reserve in 301 patients by classical stimulation tests and in 68 of these patients mean nocturnal spontaneous secretion was also measured. Spontaneous telarche and/or pubarche were present in 33% of girls aged > 9 years. In 11% of patients, weight was more than 20% above levels appropriate for height. In 36.2% of patients (low-responders), we observed a reduction of the GH reserve (peak < or = 10 micrograms/l during two stimulation tests). Moreover, we noted reduced mean nocturnal spontaneous secretion (< or = 3.3 micrograms/l) in 61.8% of patients. Karyotype and the presence/absence of spontaneous telarche and/or pubarche did not influence either GH reserve or mean nocturnal spontaneous secretion. GH secretion (both GH reserve and mean nocturnal spontaneous secretion) did not influence height, yet low-responders had a significantly higher chronological age than normal-responders. Obese Turner's girls were low-responders and showed reduced mean nocturnal spontaneous secretion more frequently than normal weight girls; body mass index was significantly higher in patients with reduced GH secretion when compared to patients with normal GH secretion. We conclude that impairment of GH secretion is frequent in Turner's syndrome patients, especially if obese; that GH secretion impairment is not related to karyotype or spontaneous telarche and/or pubarche; that GH secretion is irrelevant to growth in these, patients and, therefore, its evaluation is unnecessary.