The effects of l-propranolol, d-propranolol and clonidine on homovanillic acid (HVA) concentrations in the corpus striatum and nucleus accumbens of rats were studied under normal conditions and after treatment with oxotremorine or haloperidol. Thile propranolol and clonidine given alone had no significant effect on HVA levels in either area, l-propranolol (1--10 mg/kg) and clonidine (0.1 mg/kg), both significantly inhibited the elevation of striatal HVA, found 60 min after oxotremorine administration. Both l- and d-propranolol (2.5 mg/kg), reduced the effect of oxotremorine in the nucleus accumbens. Neither l-propranolol no clonidine affected the rise in HVA in either brain area seen after haloperidol. Our results suggest that propranolol may reduce cholinergic activation of dopaminergic pathways by two different mechanisms. One is stereospecific for the l-isomer and operates in the striatum and another, which is shared by both isomers, occurs in the nucleus accumbens.