1. No alteration in cerebral water content was observed in rats following administration of cortisol, aldosterone or the adrenal inhibitor 2 methyl \x=req-\ 1,2-di-3\m='\ pyridylpropan-1-one (SU 4885).2. Aldosterone was found to decrease the cerebral oedema produced by intravenous injection of water.3. Cortisol and SU 4885 had no effect on cerebral water content following intravenous administration of water.