Heterotranplantability of myxoma of rabbits was formely demonstrated when grafts from subcutaneous tissue in skin were used (MARGARINOS TÔRRES & RITA CARDOSOS, 1949). Better results are reported in this paper when grafts from the spleen of infected rabbits were employed. While grafts from normal spleen are almost completely absorbed in sixteen days, those from infected rabbits give origin to full-grown and vascularised tissue in which typical myxoma cells are predominant elements. Progressive growth of heterotransplantated myxoma cells is another similarity between infectious myxoma and malignant tumors. Formation of clear areas of circular contour (interference of a diffusible substance?) associated to myxomatous degeneration is very conspicuous. Peculiar changes of the ground substance, reticular and collagenous fibers (globular swelling, rosary and bulb formation) apparently related to myxomatous degeneration are described. An unexpected finding was the presence of typical intranuclear inclusion bodies in five among forty-eight grafts examined in the sixth day.