Attempts to induce gliomas in experimental hosts with at least 4 tumor viruses have been made (1, 2). Intracerebral inoculations of polyoma virus, simian virus 40 (SV40) and adenovirus 12 have been unsuccessful (1); but induction of gliomas in dogs by intracerebral inoculation of Rous sarcoma virus has been described (2). In contrast, attempts to induce in vitro transformation in glial cells by tumor viruses have not been reported. Lack of such attempts may in part be due to the fact that the usual technic for cultivation of brain tissues, by explanation of brain fragments, provides glial cells admixed with non-glial cell types (3). In this system it would be difficult to ascertain that any transformed cells that might appear were derived from glial cells. Recently, propagation of human fetal astrocytes and spongioblasts was reported in dispersed cell cultures which apparently consisted exclusively of these cell types (4). It became of interest, therefore, to study the effects of infection by a simian tumor virus (SV40) on these cells. The present communication describes SV40-induced transformation of astrocytes, SV40-induced cytolysis of spongioblasts, and certain characteristics of the transformed astrocytes.