Studies on Human Leukemia. II. Struc- ture and Quantitation of Myxovirus-Like Particles Associated With Human Leuke-

SUMMARY-A method was developed for the quantitation and examina-tion of the morphology of myxovirus-like particles found in human leukemic and infectious mononucleosis materials. The average diameter of particles from leukemic patients was 178 m ~ compared with 138 m ~ for particles from patients with infedious mononucleosis. Particles from both sources were strudurally similar to each other and to particles associated with avian and murine leukemia. However, no tail-like appendages were seen on particles from human specimens like those sometimes seen on particles associated with murine leukemias. Concentrations of over 3 X 1010 particles per ml were encountered in some human sera and plasmas. Nor-mal whole blood cells, on prolonged storage at 4 0 C, released particles remarkably similar in size and morphology to the particles seen in materials. from leukemic and infedious mononucleosis patients.-J Nat Cancer Inst 33: 557-570,1964. TISSUE CULTURE propagation and precis