This chapter discusses the isolation and binding characteristics of nuclear retinoic acid receptors. The addition of protease inhibitors, glycerol, and monothioglycerol in all buffers used during the preparation and analysis of nuclear and cytosolic extracts appears to be essential for assaying retinoic acid receptor (RAR) proteins. The omission of these substances resulted in the complete elimination of, or greatly reduced, retinoic acid-binding activity. The nuclear retinoic acid receptors are distinguished from cellular retinoic acid-binding protein (CRABP) by molecular weight, cellular distribution, and retinoid-binding characteristics. The nuclear receptors RARα, RAReβ, and RAR have a molecular weight of approximately 50,000 and are largely associated with the nucleus. Assay of [3H]retinoic acid-binding activity via size-exclusion HPLC can be used to perform saturation binding and Scatchard plot analyses in order to determine the binding affinity and number of receptors per cell. The binding characteristics of the nuclear receptors are different from those of CRABP. © 1990, Elsevier Inc. All rights reserved.