Leucocyte cytograms were obtained by using a Technicon H6000 (Technicon Instrument Corporation, Tarrytown, NY, USA) in conjunction with an automated flow-cytochemical analyser by which leucocytes can be differentiated by cytochemical (peroxidase activity) and optical (cell size) methods. By analysis of cytograms obtained in this way, we found twelve cases of lowered eosinophil peroxidase activity among approximately 600,000 blood samples-days between 1984 and 1989. Ring eosinophils were observed on the peripheral blood smears in 2 out of 12 cases. The first case was a 41-year-old female confined to hospital with Hashimoto's disease, and the other a 54-year-old female hospitalized for trauma. In both cases, the percentage of eosinophils was normal, although some had ring-shaped nuclei with a large central nuclear hole and a nuclear ring formed with a thin nuclear chromatin bridge. Ring eosinophils previously have been described in patients with hematological malignancy, hypereosinophilic syndrome or severe alcoholism. Recently we observed ring eosinophils in a healthy individual for the first time. Although ring eosinophils may not have specific diagnostic significance, these cases are reported because they displayed a rare phenomenon.