Lung volumes were measured in 45 children with chronic renal failure and compared to 10 healthy controls. Six patients were receiving conservative treatment (CT), 11 were undergoing regular haemodialysis (HD), 8 were on continuous ambulatory peritoneal dialysis (CAPD) and 20 were post transplantation (TP). We measured vital capacity (VC) and forced expiratory volume in 1 s (FEV-1) with a bell spirometer. In addition residual volume (RV) was determined in CAPD patients. VC and FEV-1 values below the lower limit of predicted normal values from healthy children with the same body height were found in 38% and 52% of all patients respectively (P less than 0.05). Median values of VC and FEV-1 were lowest in CT and highest in TP patients. Median FEV-1 was significantly reduced to 79% of predicted values in CT and to 82% in HD patients (P less than 0.05). No correlation was found between FEV-1 and haemoglobin levels or the concomitant use of beta-blocking agents. During a HD session mean FEV-1 increased significantly. In CAPD patients the routine filling of the abdomen was followed by an 11% decrease of RV (non significant) while the other parameters remained stable. It is concluded that lung volumes are frequently reduced in chronic renal failure but remain essentially stable during the dialysis procedures.