That eserine and atropine stimulate the pituitary-adrenocortical system has been proved only by indirect evaluation such as the rat adrenal ascorbic acid depletion test (Dordoni & Fortier, 1950). In the experiments of Harwood & Mason (1956) eserine was injected intravenously in a dose of 0·05 mg./kg. body weight into unanaesthetized dogs. Although a marked eosinopenia was observed, no definite rise in the level of 17-hydroxycorticosteroids (17-OHCS) in peripheral blood was found after administration of eserine. In the present study attempts were made to evaluate directly the effect of eserine and atropine on adrenal 17-OHCS secretion in unanaesthetized dogs. Six mongrel dogs weighing between 11 and 15 kg. were used. Samples of adrenal venous blood were taken from the unanaesthetized animals by a modification of the method of Satake, Sugawara & Watanabe (1927) (see Suzuki, Hirai, Yoshio, Kurouji & Yamashita, 1963). The observations were started about 18 hr. after completion of