Abstract-To determine the influence of colchicine on adrenocortical function in vivo, we gave significant amounts subcutaneously to rats and observed the distribution to the anterior pituitary and adrenal glands. Corticosteroids in the serum and adrenal gland were increased remarkably by the administration of colchicine in a dose-dependent manner.Maximum elevation was achieved around 2.5 hours after the injection and continued for at least 4 hours. Maximum levels produced by the injection of 1 mg/kg body wt. of colchicine were the same as those elicited by the injection of 0.1 U/rat of adrenocorticotropic hormone, the latter producing temporary increases in corticos teroids in the serum and adrenal gland. A significant augmentation of corticosteroids in the serum and adrenal gland resulted when colchicine was administered 60 minutes prior to the injection of adrenocorticotropic hormone. The pattern of intracellular distribution of corticosteroids in the adrenal glands of rats given colchicine was the same as that seen in rats given adrenocorticotropic hormone. In the in vitro experiment, only high concentrations of colchicine such as 10-3 M added to the incubation system of the adrenal quarters suppressed the release of corticosteroids from the adrenal gland. Thus, the continuous stimulation of the synthesis and secretion of adrenocortical hormone seen with the administration of colchicine may explain why this drug is effective in the treatment of gouty arthritis.Colchicine has long been effectively used for cases in acute gouty arthritis, but the mode of action is not entirely understood. A possible relationship between the genesis of acute gouty arthritis and inflammatory reaction of the knee joint produced by the local injection of urate crystals has been suggested (1), but colchicine administration does not produce a decrease in the concentration of uric acid in the serum or promote the excretion of uric acid. The present study was carried out to examine the influence of colchicine administration on adrenocortical function in rats in vivo. Direct effect of the agent on the release of corti costeroids from adrenal gland was also studied in the in vitro experiment.