We reported three additional cases of a newly described syndrome called episodic angioedema with hypereosinophilia. In order to investigate its pathophysiological mechanisms, four parameters were concurrently investigated, including blood eosinophil density, serum chemoattractant activity, serum major basic protein (MBP) levels and the presence of anti-endothelial cell antibodies. Distribution of eosinophils through a metrizamide density gradient showed a preferential sedimentation of blood eosinophils in intermediate layers, clearly different from the hypodense cells (low-density layers) identified in a group of seven patients with idiopathic hypereosinophilic syndrome (HES). In two of the three patients with cyclic angioedema, a chemotactic activity towards eosinophils was detected in the serum (30 +/- 6 and 42 +/- 12 eosinophils per high-power field; P less than 0.05 compared with a control group). Serum MBP levels were at 1524, 619 and 1200 pg/ml. All three patients had circulating anti-endothelial cell antibodies, predominantly of the IgG isotype, in contrast to controls (P less than 0.01) or to patients with HES (P less than 0.01). Specificity of the antibody for endothelial cells was demonstrated in the three patients studied by the absence of binding to various blood cells, including monocytes, lymphocytes, eosinophils and platelets. In one case (patient 2), the levels of anti-endothelial cell antibodies, as well as the serum chemoattractant activity to eosinophils varied according to the successive acute phases of the disease. Although further investigations are needed to clarify the exact pathophysiology of this syndrome, and especially the possible participation of the anti-endothelial cell antibodies in the cutaneous lesions, these data suggest that angioedema observed in this syndrome could result from the combined effects of activated eosinophils and of immunologically induced endothelial lesions.