AbstractCorticotropin releasing factor receptor type 1 (CRF1), a coordinator of the body responses to stress, is also expressed in human skin, where it undergoes alternative splicing. Since the epidermis is continuously exposed to the environmental stress, human keratinocytes were chosen to study the biological role of CRF1 alternative splicing. The expression pattern of CRF1 isoforms depended on cell density, presence or absence of serum, and exposure to ultraviolet irradiation (UVR). Only two isoforms α and c were predominantly localized to the cell membrane, with only CRF1α being efficient in stimulating cAMP responding element (CRE). CRF1d, f and g had intracellular localization, showing no or very low (g) activation of CRE. The co‐expression of CRF1α with d, f or g resulted in intracellular retention of both isoforms suggesting dimerization confirmed by detection of high molecular weight complexes. The soluble isoforms e and h were diffusely distributed in the cytoplasm or localized to the ER, respectively, and additionally found in culture medium. These findings suggest that alternatively spliced CRF1 isoforms can interact and modify CRF1α subcellular localization, thus affecting its activity. We suggest that alternative splicing of CRF1 may play an important role in the regulation of skin cell phenotype with potential implications in pathology. J. Cell. Physiol. 218: 593–602, 2009. Published 2008 Wiley‐Liss, Inc.