BACKGROUND: Peripheral chemoreceptors residing predominantly in the carotid body monitor changes in arterial blood oxygen and are mechanistically linked to the cardiorespiratory control by the autonomic nervous system. Enhanced sympathetic activation is common in end-stage renal disease and kidney transplantation has been shown to improve cardiorespiratory reflex measures of autonomic function. OBJECTIVE: The aim of the present study was to test whether improvement in renal function following kidney transplantation is related to an improvement in chemosensory function. METHODS AND RESULTS: We compared hyperoxic chemoreflex sensitivity (CHRS) in patients after renal transplantation (RTX) to that in patients on maintenance hemodialysis (HD), and that of age- and gender-matched healthy controls. In addition, we investigated the impact of common confounding factors including pharmacological neurohumoral modulation and diabetes mellitus. The difference in the R-R intervals divided by the difference in the oxygen pressures before and after deactivation of the chemoreceptors by 5-min inhalation of 7 L oxygen was calculated as the hyperoxic CHRS. Autonomic activity was characterized by 24-h time-domain heart rate variability (HRV) parameters. CHRS was improved in RTX patients as compared to HD patients being related to HRV. CHRS was related to the concomitant presence of diabetes and medication with cyclosporine. CONCLUSION: Our findings indicate that chemosensory activity following kidney transplantation is related to cardiac autonomic control, but functional testing might only be useful to characterize the time course and extent of sympathetic activation in selected patients due to existing co-morbidities and immunosuppressive medication in this population.