Out of 60 males aged 41 +/- 1 suffering from mild arterial hypertension (158 +/- 4/100 +/- 2 mm Hg) a hereditary load by hypertension was found in 63.3%, serum cholesterol levels reached 200 mg/dl in 85% of the patients. The patients with the load and enhanced Na-Li countertransport (403 +/- 49 mumol Li/1/cell/hr against 185 +/- 28 mumol Li/1/cell/hr in those without hereditary predisposition, p < 0.05) showed a significantly higher serum level of IgA and IgE (3.68 +/- 0.33 g/l and 127 +/- 14 U/ml vs 2.61 +/- 0.33 g/l and 79 +/- 15 U/ml, respectively, in those without the load, p < 0.01, p < 0.05). An IgE level significantly correlated with the amplitude of norepinephrine vascular reactivity (r = 0.35, p < 0.05). The discussion is concerned with IgE hyperproduction significance. Correlating with the amplitude of vascular reactivity on sympathetic stimuli and being independent of hypertension magnitude, this hyperproduction may underlie a high risk of atherosclerosis and vascular complications as a result of IgE-mediated vascular reactions in young subjects with mild hypertension in hereditary loading, erythrocytic accelerated Na-Li countertransport and lipid metabolism derangement.