BACKGROUND Respiratory functions are affected during hemodialysis. The strength of respiratory muscles, ultrafiltration rate, and acid-base balance have been suggested as important factors. L-carnitine is crucial for energy producing, utilization of fatty acid, and possible amino acids. A lack of carnitine in hemodialysis patients is caused by insufficient carnitine synthesis and especially by its loss during dialysis. This study was performed to investigate the chronic effects of L-carnitine treatment on respiratory functions in adults receiving chronic hemodialysis therapy. METHODS A total of 20 hemodialysis patients were scheduled to take L-carnitine supplementation (20 mg/kg three times/week) (group 1), and the rest of 20 hemodialysis patients served as the control group and were observed without supplementation with L-carnitine (group 2). Pre- and post-dialytic L-carnitine levels and post-dialytic respiratory functions tests were performed in both groups at baseline and after six months. RESULTS The average concentration of free and total carnitine levels increased significantly after six months of supplementation (p < 0.01). While a statistically significant increase between postdialytic forced expiratory volume in one second/forced vital capacity values after treatment period (77.10 +/- 12.15 and 83.00 +/- 14.49, before and after treatment, respectively, p < 0.05) was observed, the increase of vital capacity, forced expiratory volume in one second, and forced expiratory flow between 25-75% of expired vital capacity were not significant in the treatment group (p > 0.05). CONCLUSIONS Intravenous L-carnitine supplementation could contribute to the management of respiratory dysfunction in chronic hemodialysis patients by improving FEV1/FVC. The mechanism by which LC causes these effects merits further investigation.