The effect on rat striatal membranes of continuous treatment (40 days) and withdrawal for 5, 10 and 20 days of haloperidol (2 mg/kg), thioridazine (25 mg/kg) and clozapine (30 mg/kg) was studied. Using 1,6-diphenyl-1,3,5-hexatriene no significant changes in fluorescence polarization was observed, but on using 8 anilino-1, naphthalene sulphate marked changes were observed and fluorescence polarization decreased after continuous treatment with haloperidol and thioridazine but increased after clozapine. However, following withdrawal, the fluorescence polarization increased in haloperidol and thioridazine groups returning to normal by the 20th day of withdrawal; whereas following clozapine withdrawal it normalised by day 5 and remained unchanged thereafter. Striatal acetylcholineesterase activity also showed marked changes, and decreased after continuous treatment with the three drugs. However, the activity returned to normal after clozapine and thioridazine withdrawal but increased after haloperidol withdrawal. Thus, the three drugs appear to exert a distinct effect on the striatal membranes after continuous treatment, which on withdrawal, normalises earlier in thioridazine and clozapine than haloperidol treated rats.