JHM virus (JHMV) and A59 virus (A59V) are neurotropic members of the hepatoencephalitis group of murine coronaviridae. JHMV has a markedly greater neurotropism for weanling BALB/c mice than does A59V. Both viruses display one-hit kinetics when grown in vitro in 17CL-16 cells, a clone of BALB/c3T3 cells. Virus-specific intranuclear, cytoplasmic, and surface antigens have been observed for both viruses by immunofluorescence. The intranuclear antigen appears first at about 2 hr after infection (hpi) followed by the development of the cytoplasmic and surface antigens at 3 hpi at 38.5°. Most, if not all cells that develop the intranuclear antigen, produce cytoplasmic antigen and presumably progeny virus. Progeny virus production is independent of cell fusion and formation of syncytia. Virus-specific ribonucleoprotein is synthesized in the presence of 1 μg/ml actinomycin D, a concentration sufficient to inhibit the synthesis of cellular ribonucleoprotein species that have sedimentation properties similar to the virus-specific species. The virus-specific ribonucleoprotein species that is resistant to 10 mM EDTA, presumptive virion ribonucleoprotein, has a sedimentation value in sucrose of about 230 S for JHMV and 200 S for A59V. The species of virus-specific ribonucleoprotein that are sensitive to 10 mM EDTA presumptive messenger ribonucleoprotein, are about 40–100 S in sucrose for both viruses. The purified presumptive virion RNA is about 50 S in sucrose for both viruses. The major species of presumptive mRNA of both viruses is about 18 S with secondary species of about 28 S in sucrose. Denaturation of the virus-specific RNA with heat and dimethylsulfoxide does not appreciably alter the sedimentation profiles of either the presumptive virion RNA or mRNA species.