Intraperitoneal injection of mammalian adrenocorticotrophic hormone at 2 IU and 4 IU per day for seven days was followed by hyperglycemia and adrenal growth in goldfish. Normal blood sugar values, at 16°–20°C, were about 30 mg% by both Folin and Glucostat methods. Mcan values after treatment approached 70 mg%. Hypertrophy and hyperplasia of interrenal tissue were seen in most treated fish. Nuclear pycnosis and cell shrinkage were infrequent. Control and experimental populations showed no differences in frequency of nucleolar extrusion.