To determine the effects of nonventilatory CO₂ transfer on breathing pattern, we monitored breathing in 7 patients with renal failure undergoing hemodialysis. A respiratory inductance plethysmograph was used to record ventilation before and during dialysis. The duration of inspiration (T_I), the duration of each breath (T_Tot) and the duty cycle (T_I/T_Tot) did not differ for the pre-dialysis and the dialysis periods. In contrast, for each patient the mean tidal volume (V_T) fell significantly during dialysis (p < 0.05), accounting for the reduction in minute ventilation (p < 0.005). The mean inspiratory flow rate (V_T/T_I) also fell (p < 0.01), demonstrating that nonventilatory CO₂ loss via the dialysis bath is associated with reduced respiratory drive.