Liver tumor biopsies of a 9-year-old moribund Tupaia (tree shrew) were explanted and cultured in vitro. The cell cultures degenerated spontaneously. A virus was isolated from the cell-free supernatant of these cultures and subsequent electron microscopy revealed rhabdovirus-like particles. Negative staining showed typical bullet-shaped particles 125-220 nm in length with a diameter of 68 nm studded with a dense layer of surface projections 9-11 nm in length. One end of the virion was flat, the other end was open; a distinct ribonucleoprotein (RNP) core was visible. The pitch of the RNP was 4.5 nm. Virus was assembled and matured by budding primarily into regions of dilated endoplasmic reticulum. The dimensions of the virion also were determined in ultrathin sections: the diameter and length of the virion were 52 and 125-255 nm, respectively, those of the RNP core were 39 and 120-240 nm. Only tupaia embryonic fibroblasts and kidney cells were susceptible to the rhabdovirus. The virus, when plaque-assayed on tupaia embryonic fibroblasts, grew to a titer of 1 X 10(6) PFU.