Hypothalamic pituitary function was studied in 13 patients with myasthenia gravis. Gonadotropin, TSH, and prolactin dynamics were investigated using conventional provocative stimuli. No consistent abnormality was found in either gonadotropin or prolactin release. Abnormal TSH responses to TRH administration was present in six of the 13 patients in association with normal free thyroxine indices and the absence of antithyroid antibodies. This latter observation is relevant when the association of myasthenia gravis with hyperthyroidism, thyroiditis and hypothyroidism is considered.