Hormone production in a patient suffering from a late recurrence of a granulosa cell tumour has been studied pre- and post-operatively, and a vein on the tumour surface was cannulated at operation to collect tumour vein blood for pre-operative studies. Elevation in the plasma oestradiol level and depression in FSH and LH were found pre-operatively, and elevations were found in tumour vein oestradiol and 17α-hydroxyprogsterone. Plasma oestradiol level returned to normal postoperatively whereas FSH and LH levels were persistently depressed. FSH receptors were found in this tumour, and on the basis of this finding, gonadotrophins were given to athymic nude mice in an attempt to support the growth of the granulosa cell tumour implanted in these animals. We demonstrated that gonadotrophins have supported the tumour tissue, but not promoted growth.