Continuous ambulatory peritoneal dialysis (CAPD) often leads to better control of hypertension. In order to evaluate the effects of such improved blood pressure control on left ventricular (LV) hypertrophy and LV function, a group of 18 patients with a history of hypertension were followed for changes in LV anatomy and function (with M-mode echocardiography) over a 6 to 12 month period after initiation of CAPD. All patients had echocardiographic evidence of increased LV mass related to concentric and eccentric hypertrophy. On CAPD, blood pressure decreased (greater than 5 mm Hg) in 12 patients. LV mass decreased in 15 patients and increased in one. A decrease in both wall thickness and LV dimension contributed to the fall in LV mass on CAPD. Initially, LV dimension exceeded normal in 9 out of 18 patients. On CAPD, LV dimension decreased to near normal in size in six, and no patient developed LV dilation on CAPD. Four patients initially had a decreased fractional shortening and ejection fraction; three of these normalized while on CAPD and no patient deteriorated. These results indicate that CAPD improves LV hypertrophy by normalizing both volume and pressure overload. These effects may prevent deterioration in LV function in patients with still normal LV function, and may improve LV function in patients who already exhibit decreased LV performance.