The density of alpha 2-adrenoceptors was determined in different forebrain regions of lean and obese Zucker rats by para-[125I]iodoclonidine ([125I]PIC) receptor autoradiography. No significant differences were observed between the Zucker phenotypes in the density of alpha 2-adrenoceptors in any brain areas examined. Four days treatment with the antiglucocorticoid mifepristone (RU 38486) did not affect [125I]PIC-binding. It is concluded that the hyperphagia and abnormal corticosterone secretion of genetically obese Zucker rats do not appear to be associated with changes in alpha 2-adrenoceptor density in brain.