In membranes prepared from rabbit liver, competition with [3H]prazosin by different alpha 1-agonists and antagonists revealed different affinities in comparison to the results obtained on rat liver membranes, and showed a good correlation with the affinity of the same compounds for the cloned alpha 1c-adrenoceptor subtype. The potencies observed on rat liver membranes were well correlated with the affinity observed for the cloned alpha 1b-adrenoceptors. These results confirm that rabbit and rat liver membranes preparations can be utilized to evaluate the affinity of compounds for these alpha 1-adrenergic subtypes.