Hydrocortisone treatment caused a hyperglycaemic state in Clarias batrachus within an hour. The blood glucose values remained significantly increased for 6 days. An initial increase in liver glycogen was followed by a decrease below the normal value. The muscle and brain glycogen levels remained unaffected. A mild degranulation of B cells was seen in the early hours and a conspicuous vacuolation and necrosis of both A and B cells appeared 72-96 h after treatment. Administration of thyroxine resulted in hyperglycaemia within 15 h but a distinct hypoglycaemic condition was seen 4 days after the treatment. Considerable drain in the liver glycogen deposits was noticed between 24 and 72 h while the muscle glycogen showed an increase. The brain glycogen did not change noticeably. Islets of the fishes autopsied between 72 and 96 h contained severely damaged B cells. The A cells remained unaffected. It is suggested that, in addition to several other hormones, hydrocortisone and thyroxine play an important role in carbohydrate metabolism and blood sugar homoeostasis in C. batrachus.