Cells were obtained from the peripheral blood of a patient with marked non-leukaemic eosinophilia. Transmission electron microscopy (TEM) showed typical mature eosinophils. The surface architecture of eosinophils by scanning electron microscopy (SEM) shows that most were spherical with varying numbers of microvilli; a smaller proportion of cells had ridge-like profiles, small ruffles and occasionally blebs. The surface features of the eosinophil thus resemble most lymphocytes and this finding must be considered when leucocyte populations are examined by SEM.