An FSH-secreting pituitary adenoma was demonstrated in a 32-yr-old man who presented with unilateral optic atrophy without any clinical or laboratory evidence of hypogonadism. Semen analysis was normal, although basal FSH levels were markedly elevated (>80 mlU/ml). He had normal plasma LH levels and no other detectable endocrine abnormalities. Administration of GnRH elicited delayed and sustained FSH and brisk LH responses. Administration of TRH resulted in TSH and PRL responses and unexpected FSH and LH elevations. Two surgical operations resulted in temporary reduction of plasma FSH levels, but it increased later concomitant with CT demonstration of tumor growth. After pituitary irradiation, no reduction in FSH levels occurred. A single dose of 5 mg bromocriptine elicited a significant reduction in FSH levels from 137 to 64 mlU/ml. Long term treatment with 15 mg/day bromocriptine resulted in further reduction of FSH level, to 36.4 mlU/ml, without any change in tumor size. This finding implies that bromocriptine could be an adjunctive therapy or an alternative to other modes of treatment in patients with these rare tumors.