The aim of the present study was to delineate the involvement of TRH receptors in the thyrotrope adaptation to starvation (i.e. plasma TSH and thyroid hormone decrease, increased sensitivity to T3) by measuring [3H]TRH binding in euthyroid, hypothyroid and T3-substituted rats (175 ng/100 g body weight). Our results show that in euthyroid rats, starvation does not significantly modify either the affinity or the number of pituitary binding sites. In hypothyroid and T3-substituted rats, starvation does not alter the negative control exerted by T3 on the number of TRH binding sites. Our data indicate that the adaptation of thyrotrope to starvation does not primarily result from alterations of TRH binding sites.