Renal erythropoietin production is dependent on local oxygen content of blood which activates so called "oxygen sensors". Taking into consideration altered local renal blood supply in patients with arterial hypertension in the course of arteritis (HA) and from the other side contribution of the renin-angiotensin system in both pathogenesis of hypertension and regulation of erythropoietin production it seemed plausible to undertake this study. The aim of the study was to determine whether and in what extent patients with HA and healthy subjects differ in EPO secretion and whether EPO serum level is related in this patients to renin response to dietary sodium restriction and upright position of the body. 18 patients with HA and 12 healthy subjects were investigated. In all subjects haematocrit value, haemoglobin concentration, erythrocyte count, sodium, potassium, creatinine, iron, ferritin serum levels, total iron binding capacity, plasma renin activity (PRA), erythropoietin serum level and mean arterial blood pressure (MAP) were measured in basic conditions (normal sodium diet). Additionally PRA, EPO and MAP were measured after dietary sodium restriction to 10-20 mmol Na/24 hrs for three days and upright position of the body for three hours. Patients with HA had insignificantly lower serum EPO concentrations than healthy subjects and both studied groups did not differ in haematocrit value and determinants of iron metabolism except of significantly higher ferritin concentration in HA. After dietary sodium restriction and upright position of the body significant rise in PRA and no significant changes in EPO level were found in studied groups.(ABSTRACT TRUNCATED AT 250 WORDS)