Immunophilin FKBP51 assists polypeptide folding, participates in glucocorticoid actions and may play a role in glucocorticoid resistance. FKBP51 is altered in patients with asthma, but its role in chronic obstructive pulmonary disease (COPD) characterized by dysregulation of several pro/antiinflammatory genes is less clear. We assessed changes in nuclear/cytosolic FKBP51 protein using SDS-PAGE/WB and FKBP51 mRNA by qRT-PCR in cells isolated from induced sputum of stable COPD patients treated with formoterol/budesonide or formoterol/budesonide/theo?phylline for 4 wk. Expression of FKBP51 was higher in formoterol/ budesonide/theophylline-treated patients, compared with formoterol/budesonide group in both cytosolic and nuclear fractions by about 57% and 31%, respectively (P<0.001, P<0.01). FKBP51 mRNA was only slightly, but not significantly, higher in patients on formoterol/ budesonide/theophylline. Increased FKBP51 in COPD patients treated with formoterol/ budesonide/theophylline may be important in altering signaling from corticosteroid receptors.