The aim of the present investigation was to discover whether disturbed left ventricular (LV) function limits renal replacement therapy in patients with juvenile onset diabetes mellitus. Seventeen patients given functioning kidney grafts were studied non-invasively (M-mode echocardiography, apexcardiography, phonocardiography) before renal transplant and an average of six, 13 and 44 months after transplant. The main pretransplant findings were pronounced LV hypertrophy with impaired diastolic LV function (prolonged relaxation time + signs of decreased LV distensibility) and a hyperdynamic circulation. Most of these abnormalities were significantly less severe after successful kidney transplantation. LV mass decreased by 37% 44 months after transplant (p less than 0.01) and LV diastolic and systolic volumes decreased with a subsequent increase in ejection fraction from 0.65 to 0.78 (p less than 0.01). The LV distensibility and filling pattern improved significantly while the prolonged relaxation time was unchanged. These findings imply that pretransplant disturbances in LV function are related more to factors such as hypertension, volume overload and uraemia than to diabetes per se because no pronounced improvement in the metabolic disorder resulting from diabetes can be expected, even after the most successful transplant. Disturbed LV function should not, therefore, exclude uraemic diabetics from renal replacement.