The ultrastructural pattern of biopsies of two cases of Colombian Burkitt's lymphoma is studied. Epstein Barr viruses were found in tissue cultures form one of these two cases and their morphology and biological behavior are compared with tissue cultures derived from an African case, JIYOYE cell line,. Several experiments performed with the JIYOYE cell line, and based in the effect of different temperatures on the synthesis of EB virus by the cultured cells, resulted in the obtention of a cell line free of virus and with high titers of IgG.