New World primates express a form of sterol/steroid resistance resulting from the presence of a 58–60 kDa intracellular protein (IDBP) which competes with nuclear receptor proteins for binding of vitamin D metabolites and sex steroids. As the thyroid hormone receptor is a recognized member of the steroid/retinoid/vitamin D receptor gene superfamily, we sought to confirm previous data describing the existence of thyronine resistance in New World primate species and to determine whether IDBP was capable of binding ligands which confer transcriptional regulatory potential on thyroid hormone-retinoid heterodimeric complexes. Circulating thyroid hormone levels were compared between vitamin D-resistant New World primates and nonresistant Old World primates. Total triiodothyronine (T3), free T3 index, and free thyroxine were not different between New World and Old World primates. Thyroxine was significantly lower (P < 0.03) in New World than in Old World primates. T3 (1 pM-1μM), 9-cis retinoic acid (100 nM) and all-trans retinoic acid (100 nM) were incapable of displacing 2 nM [3H]25-hydroxyvitamin D3 from IDBP extracted from B95-8 cells, a B-lymphoblastoid cell line derived from the vitamin D-resistant New World primate Callithrix jacchus. We conclude that the sterol/steroid-resistant state characteristic of many genera of New World primates does not extend to thyroid hormones and that the IDBP responsible for vitamin D resistance does not bind T3, 9-cis retinoic acid, and all-trans retinoic acid. © 1994 Wiley-Liss, Inc.