Immunophilins comprise a family of intracellular proteins with peptidyl-prolyl-(cis/trans)-isomerase activity. These foldases are abundant, ubiquitous, and able to bind immunosuppressant drugs, from which the term immunophilin derives. Family members are found in abundance in virtually all organisms and subcellular compartments, and their amino acid sequences are conserved phylogenetically. Immunophilins possess the ability to function as molecular chaperones favoring the proper folding and biological regulation of their biological actions. Their ability to interact via their TPR domains with the 90-kDa heat-shock protein, and through this chaperone, with several signalling cascade factors is of particular importance. Among the family members, the highly homologous proteins FKBP51 and FKBP52 were first characterized due to their ability to interact with steroid hormone receptors. Since then, much progress has been made in understanding the mechanisms by which they regulate receptor signaling and the resulting roles they play not only in endocrine processes, but also in cell architecture, neurodifferentiation, and tumor progression. In this article we review the most relevant features of these two immunophilins and their potential as pharmacologic targets. Fil: Erlejman, Alejandra Giselle. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales; Argentina Fil: Lagadari, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; Argentina Fil: Harris, Diondra C.. University Of Texas At El Paso; Estados Unidos Fil: Cox, Marc B.. University Of Texas At El Paso; Estados Unidos Fil: Galigniana, Mario Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; Argentina