The course of left ventricular hypertrophy was investigated in anemic hemodialysis patients treated with recombinant human erythropoietin (r-huEPO). 12 patients, aged 60.8 ± 9.9 years (mean ± SD) were treated for 18.8 ± 2.7 months. Left ventricular size was estimated by echocardiography performed before treatment and at least 12 months after relieving anemia. Patients had signs of left ventricular and/or asymmetric septal hypertrophy when compared with a nonanemic and normotensive control group matched for sex and age. At baseline, hemoglobin (Hb) was 8.6 ± 0.7 g/dl; interventricular septum thickness (IVST) was 1.75 ± 0.34 cm, left ventricular posterior wall thickness (LVPWT) 1.32 ± 0.19 cm, left ventricular muscle mass index (LVMI) 222.7 ± 41 g/m2 and blood pressure (BP) 146.4 ± 10/81.6 ± 6 mm Hg. Hb rose to 11.4 ± 1.2 g/dl (p < 0.001); IVST and LVMI decreased to 1.42 ± 0.35 cm (p < 0.02) and 155.4 ± 25.1 g/m2 (p < 0.001); LVPWT and BP remained unchanged (1.30 ± 0.26 cm and 146.8 ± 16.9/81.2 ± 7.8 mm Hg) at the end of the study. During the observation period, two groups of 5 and 7 patients differed from each other. The group of 5 patients had higher BP values (158.9 ± 9.8/86.5 ± 5.3 vs. 140.0 ± 9.5/79.2 ± 6.8 mm Hg, p < 0.01nd the period with Hb values above 10 g/dl was shorter (14.5 ± 2.4 vs. 17.8 ± 2.4 months, p < 0.05). These 5 patients failed to show a significant decrease in IVST and LVMI. We conclude that long-term amelioration of anemia in hemodialysis patients is able to induce a regression of left ventricular hypertrophy. However, inadequate BP control may compromise this effect in patients