IGF-I, testosterone and estradiol levels were evaluated in 8 girls with androgen insensitivity immediately before and from 1 to 3 months after bilateral gonadectomy. In 6 patients GH secretion was evaluated before and after gonadectomy by means of an arginine test and in 3 a sleep test was also performed. Mean IGF-I level before surgery was significantly higher than that of normal controls (2850 ± 1230 vs 1680 ± 1040 U/l, p < 0.025). After gonadectomy a significant decrease was evident for testosterone, estradiol and IGF-I levels. A positive correlation between IGF-I and estradiol levels was present before surgery (p < 0.005). The presence of a correlation with estradiol, but not with testosterone, and the knowledge that this syndrome is due to an insensitivity to androgens, but not to estradiol, support the hypothesis that the estradiol level is the major determinant for the control of IGF-I values in these patients. After gonadectomy, a substantial decrease of the 12-h nocturnal GH secretion was evident. Comparison of the nocturnal GH levels before surgery of the 3 patients with those of normal subjects of the same age showed hormonal values higher than 1 sd over the mean values of control subjects. Even if the number of patients studied is too small to draw any definitive conclusion, these data may suggest that sex hormones play a role in the control of IGF-I levels, a function which seems to be mediated through GH secretion.