We assessed the influence of hyperoxemia on erythropoietin secretion in patients with various etiological forms of arterial hypertension (essential, n = 15; renoparenchymal, n = 16; renovascular, n = 15) and in 15 healthy subjects. On the first day of the study, blood was withdrawn at 1-hour intervals for the estimation of erythropoietin during a total of 6 hours and at 2-hour intervals for the assessment of PO2. Three days later the same parameters were assessed again at identical time intervals, but the subjects were breathing pure oxygen during the first 2 hours. Breathing with pure oxygen resulted in a significant increase of blood PO2 (184.85 +/- 4.47 versus 85.92 +/- 2.28 in essential, 185.21 +/- 5.52 versus 84.55 +/- 3.04 in renoparenchymal, and 181.7 +/- 3.14 versus 87.49 +/- 2.25 in renovascular hypertension groups and 189.84 +/- 5.2 versus 85.89 +/- 1.73 mm Hg in healthy subjects; P < .001 in all groups). Baseline plasma erythropoietin was not different among the groups (29.33 +/- 4.14 in essential, 24.56 +/- 3.09 in renoparenchymal, and 27.77 +/- 3.29 in renovascular hypertension groups and 24.23 +/- 2.70 mU/mL in the control group). The pattern of erythropoietin decline was different in the groups of hypertensive patients. In patients with essential hypertension, unlike in healthy subjects and patients with other etiological forms of arterial hypertension, only a very short-term suppression of erythropoietin levels was observed during hyperoxemia. No significant changes in blood pressure during breathing with pure oxygen were found in any of the studied groups.(ABSTRACT TRUNCATED AT 250 WORDS)