Even in the absence of clinically apparent seizures, patients undergoing chronic dialysis often exhibit abnormal EEG activity, which is usually attributed to the type of dialysis or to the dysequilibrium syndrome. To find out whether these abnormalities occurred only during dialysis sessions, 10 children with end-stage renal failure undergoing chronic dialysis were continuously monitored for 52 h during dialysis and between two sessions. The EEG tracing was abnormal in 5 children. Two had paroxysmal aspecific slow waves towards the end of the sessions, with a fall in blood pressure, malaise and fainting. In 3 children EEG abnormalities - also present in the interdialytic period - were not clinically apparent. Long-term EEG monitoring in these cases distinguished between the electrical events that were related to dialysis and those that were not. It also suggested that, rather than being dialysis-dependent, these events frequently reflect a basic neurological disorder.