ALTHOUGH several studies have recently been reported on the effect of different depressant, tranquillizer and antidepressant groups of drugs on the brain microsomal ATPase (ATPphosphohydrolase, EC 3.6.1.3) system (SQUIRES, 1965; TARVE and BRECkrrLovA, 1967; ISRAEL and SALAZAR, 1967), there is, at present, relatively little information on the effect of convulsant drugs on this important brain enzyme which has been implicated with active ion transport (SKOU, 1965), neuronal excitability and associated nervous activity at the membrane level (QUASTEL, 1965). The present communication reports the effect of strychnine treatment, under in vino and in vitro conditions, on the ATPase activity of brain microsomes. These results suggest a possible role of brain microsomal ATPase in the convulsant effects induced by strychnine.