A 37-year-old man with Noonan's hypopituitarism is described. The patient had small stature, minor facial abnormalities, cubitus valgus and pectus excavatum. In addition, endocrine testing revealed deficiencies of growth hormone, gonadotrophins and TSH. Prolactin increased normally in response to TRH administration, but failed to rise after chlorpromazine. Although intrinsic pituitary dysfunction cannot be excluded, the dissociated response of prolactin to TRH and chlorpromazine suggests that the pituitary hormone deficiencies may be secondary to hypothalamic dysfunction.