Fourteen Center hemodialysis (CHD) patients, 13 continuous ambulatory peritoneal dialysis (CAPD) patients, and 10 normals matched by group for age and sex were compared using a battery of evoked (EP) and event-related (ERP) brain potential measures to determine the effects on central nervous system (CNS) functioning of these two dialysis modes. While some differences were observed in early brainstem EP waves, the majority of differences occurred in the later waves associated with higher levels of cognitive processing. With tasks involving easy discriminations, CHD patients had longer latencies, indicative of less efficient cognitive processing, than CAPD patients who resembled controls. With difficult tasks, both CHD and CAPD groups showed abnormally-delayed later components. Similar results were obtained for the amplitude of the middle latency N1-P2 component, that is, reduced amplitudes for the CHD group with respect to both CAPD and control groups under low task demand, while both dialysis groups had reduced amplitudes under high task demand. These results suggest that CAPD patients are more similar to normals than CHD patients in ERP indices of attention and the efficiency of cognitive processing.