In some hypertensive haemodialysis (HD) patients, blood pressure rises further during ultrafiltration (UF). We investigated seven such patients, who were not responsive to hypotensive drugs, including converting enzyme inhibitors. All had marked cardiac dilatation, but most were non-oedematous. They were treated with repeated intense UF while monitoring cardiac function by echocardiography. After a variable time period they all. became (near) normotensive without medication. Mean systolic and diastolic blood pressure decreased by 46+/-18 and 22+/-9 mmHg respectively while bodyweight decreased by a mean of 6.7+/-3.0 kg. Plasma volume decreased by 22%, and mean albumin increased from 3.9+/-0.3 to 4.2+/-0.3 g/dl. Cardiothoracic index decreased from a 0.56+/-0.02 to 0.45+/-0.03. Mitral and tricuspid insufficiency was present in four patients and improved or disappeared in all of them. Diameters of the inferior vena cava, left atrium, and end systolic and diastolic left ventricle markedly decreased in all patients. Ejection fraction increased, but remained subnormal in some patients, while cardiac output increased in five and decreased in two patients. We conclude that paradoxical blood pressure rise with UF usually occurs in the presence overhydration and cardiac dilatation and should be treated by intensified UF. The explanation of this phenomenon remains speculative.