In 20 patients with chronic renal failure on a hemodialysis with acetate-containing dialysing fluid gasometric, ventilation and breathing patterns disturbances were determined. The loss of CO2 in the dialysate is attributed the major cause of hypoxemia due to alveolar hypoventilation. Hemodialysis with bicarbonate-containing dialysate can be performed in the absence of any change in ventilation and PaO2 despite a systemic alkalosis. Hyperventilation during HD with high concentration of bicarbonate indicate that changes in CO2 tension in the pulmonary circulation can lead to a change in minute ventilation due to the presence of slowly adapting pulmonary chemoreceptors. In patients with low respiratory response, respiratory muscle weakness intensified additionally by hypercapnia may explain this phenomenon.