Leucocytes were isolated from the peripheral blood of normal individuals and prepared for SEM observation. The addition of the buffer Hanks and Hepes to the glutaraldehyde fixative was found to maintain the initial ambient pH throughout cell manipulation, and to allow satisfactory preservation of surface architecture.

SUMMARY Normal human leucocytes, successively treated with glutaraldehyde‐tannic acid‐osmium tetroxide‐thiocarbohydrazide‐osmium tetroxide‐thiocarbohydrazide‐osmium tetroxide, were prepared for scanning electron microscopy observation. These cells produced well‐contrasted, non‐charging scanning images compatible with metal‐evaporated material. Further, the mononuclear and polymorphonuclear cells resisted shrinkage during dehydration and critical point drying, thus allowing much improved images at high magnification than those covered with evaporated metal. In all cases at least a second thiocarbohydrazide‐osmium tetroxide treatment could not be avoided.

It is suggested that the use of Hanks' +pipes + sucrose buffers, in combination with glutaraldehyde and osmium tetroxide fixatives, represent an excellent mode of preparation of fresh and cultured peripheral blood leucocytes, not only for transmission electron microscopy observation of these cells but also for scanning electron microscopy. I N T R O D U C T I O NMeticulous studies of the preparatory conditions of human peripheral blood leucocytes are of utmost importance for proper scanning electron microscopy (SEM) investigation of cell surface architecture or transmission electron microscopy (TEM) observation of ultrastructural cellular characteristics. We have recently reported on what we believe represent quite advantageous chemical combinations in the treatment of human peripheral blood leucocytes for SEM studies (Lalague et al., 1982;Corvellec et al., 1983); the buffer-fixatives used for the SEM preparations were found to be not only quite efficient for these experiments, but also suggested their possible use in the preparation of cultured, normal human leucocytes for TEM examination. The purpose of this brief communication is to report on the use of Hanks'-pipes buffers, and their advantage, in the general treatment of leucocytes for T E M examination.

SEM observation of acute myeloblastic leukemia cells, incubated for 20 h with the mitogens pokeweed and phytohaemagglutinin, showed these to have elongated structures that were either smooth or partially covered by thumblike figures. By contrast, the chronic lymphocytic leukemia cells possessed more compact shapes and some were covered with blebs of varying sizes.