LH-RH and HCG stimulation tests were performed in a prepubertal 13-year-old boy with Noonan's syndrome. The basal plasma LH (0.8 mIU/ml) was normal and FSH (2.5 mIU/ml) high, with an elevated response of both LH (8.3 mIU/ml) and FSH (9.6 mIU/ml) to LH-RH, as seen in primary hypogonadism. However, the patient had a normal testosterone response to HCG (437 ng%). These conflicting test results illustrate the difficulty of predicting potential for fertility in patients with Turner phenotype male.