1. Data are presented on the survival time of the wallaby, Setonyx brachyurus (Quoy & Gaimard), subjected to double adrenalectomy in a two-stage operation. Animals maintained on a normal diet after the second operation had a mean survival time of 36 hr. Treatment with 1% saline, injections of whole cortical extract, and of deoxycorticosterone acetate increased the mean survival time to 91, 83 and 108 hr. respectively, but did not maintain life indefinitely. 2. The typical symptoms following the removal of the second adrenal were increasing anorexia, muscular weakness and eventual collapse, with convulsive seizures during the collapsed state in some cases. 3. Determinations of plasma sodium and potassium values showed a marked decline in plasma sodium, and a rapid rise in plasma potassium during the terminal stages. Blood glucose generally fell to low levels, while chloride fell sharply in some cases and tended to rise and then fall again in others. 4. These results are compared with the findings reported on the American opossum, Didelphis virginiana.