Circulating levels of eosinophil cationic protein (ECP), an eosinophil-specific granule protein, and peripheral eosinophils were determined in 56 patients with uremia. The patients were on a chronic hemodialysis or CAPD program or treated with diet only. They had normal counts of peripheral eosinophils but on average a threefold increase of the serum ECP concentrations compared with healthy subjects. The intracellular content of ECP in eosinophils isolated from 6 patients on maintenance hemodialysis was normal. The management or duration of the uremic condition did not influence the circulating ECP levels or eosinophil counts. Neither was any relation found between total IgE levels and peripheral eosinophils or serum ECP. The present results are compatible with an accelerated turnover of peripheral eosinophils in uremia. Such a proposed abnormal eosinophil homeostasis should demand an accelerated marrow eosinophil production, thereby explaining the previously reported marrow eosinophilia in azotemic patients.