Abstract
A mixed culture cytopathogenic effect with the development of multinucleated giant cells in feline leukemia virus-infected cultures after cocultivation with XC cells is described. This cytopathogenic effect has been utilized as a convenient visual marker for the detection and assay of feline leukemia virus in feline and canine embryo fibroblasts as well as in a canine tumor cell line, M-132-1. Comparison of the cytopathogenic reaction in the three cell lines indicates that the reaction is more rapid and pronounced in M-132-1 cells than in the embryo fibroblast cultures.