Abstract: In 7 normotensive rats intraperitoneal injections of guanethidine 15—30mg/kg thrice a week for 3 weeks exerted little influence on the systolic pressure. In 6 DOCA hypertensive rats the same dose schedule yielded a "net % of hyper- and hypotensive areas" of -1%, whereas the "net %" in 5 rats of the control group amounted to 9%. Notwithstanding that the difference between the 2 groups was statistically non-significant, evidence was suggestive that guanethidine tended to inhibit the hypertensive response to DOCA. Intraperitoneal injection of guanethidine 20mg/kg caused a marked reduction of circulating eosinophils (18 normal rats) and adrenal ascorbic acid content (15 normal rats), though the change of adrenal cholesterol content was not significant. These results indicate that guanethidine may have some influence on the adrenal cortical function.