High affinity binding sites for the potent LHRH agonist [125I][D-Ser(TBU)6, des-Gly-NH2(10)]LHRH ethylamide are present in dissociated rat testicular interstitial cells, a preparation rich in Leydig cells. The iodinated LHRH agonist binds to a single class of high affinity sites at a KD value of 0.12 nM and the number of binding sites is approx. 2500 per interstitial cell. A close correlation is observed between the potency of representative LHRH agonist to stimulate LH release in anterior pituitary cells in culture and their affinity for the testicular binding sites. The presence of specific LHRH receptors in an enriched population of Leydig cells suggests that these receptors could play a role, not only in the antifertility effects of LHRH agonists, but also in the physiological control of testicular functions.