From previous clinical and experimental observations with animals it is clear that the exophthalmos producing factor (EPF) is not the only factor which is responsible for endocrine orbitopathy. Therefore, a study of the effect of ACTH, cortisol, adrenaline, testosterone, oestradiol and oestriol on experimental exophthalmos in fish was made. Preliminary investigations were also made with a view to finding the most suitable medium of administration of drugs to goldfish and the minimum quantity of EPF that can produce a definite exophthalmos. Two doses of 0.25 mg TSH in 0.7% sodium chloride solution were found to be most suitable for obtaining a minimum but definite exophthalmos. TSH in combination with ACTH and testosterone had a synergistic effect while oestradiol and cortisol were found to inhibit the action of EPF. Adrenaline produced exophthalmos which lasted for a short time; this effect is probably due to its vasoconstrictor action. Progesterone produced exophthalmos and in combination with EPF, their effects were additive. These results show that disturbances in the regulation of different hormones can produce endocrine orbitopathy.