This small open study in elderly patients with essential hypertension investigated the effects of the angiotensin II AT1 receptor antagonist on red blood cell haematology and haemorheology. Administration of losartan over a 1-year period was not associated with a significant reduction in haemoglobin or plasma erythropoietin (EPO) concentrations and haemorheological indices remained unchanged. These findings are in contrast to similar studies with angiotensin-converting enzyme (ACE) inhibitors that have shown a significant reduction in erythropoietic activity and a decrease in blood viscosity. Our results indicate therefore that blocking the angiotensin II AT1 receptor does not affect erythropoiesis. Losartan has no adverse haemorheological effects and was associated with a small and statistically insignificant decrease in blood viscosity.