Impulse formation and conduction disturbances of the heart were investigated in 23 uraemic patients with transvenous and oesophageal electrodes. Utilizing regular atrial pacing the sinoatrial conduction time (SACT) was obtained and sinus automaticity was evaluated by measurement of the sinus node recovery time (SNRT). The atrial effective refractory period and the Wenckebach point were also determined. The effects of regular haemodialysis treatment on impulse formation and propagation disorders caused by uraemia were observed. In 16 patients transitory or permanent cardiac stimulation had to be carried out because of 2nd and 3rd degree AV block. No complication was observed during simultaneous haemodialysis and pacemaker treatment. It is concluded that the non-invasive, simple bedside oesophageal atrial stimulation method is a good alternative and should be used in the exact diagnosis of heart conduction disturbances of haemodialysed patients.