Equine herpes (abortion virus EAV) has been adapted to tissue culture (In Vitro) and to the Syrian hamster (In Vivo). In the latter, infection results in rapidly lethal hepatitis and marked viremia, up to 10 to the 11th power particles/ml of blood. The growth curves (In Vitro and In Vivo) are practically identical and permit the two systems to be compared in a unique way. Purified virus and sub-viral particles obtained by gentle means will be analyzed by polyacrylamide gel electrophoresis (PAGE) and special staining techniques to determine the protein, lipoprotein, and glycoprotein composition. Viral particles assembled in tissue culture in the presence of FUdR are noninfectious and have incomplete nucleoids (judged by electron microscopy) will be characterized as above. In particular the amount, size, and physical characteristics of viral DNA will be examined by standard techniques. The transcription of the viral genome in the presence and absence of FUdR will be investigated by hybridization. The processing of EAV-RNA is amenable to analysis, and the Poly A content of the transcripts will be determined. During infection cellular DNA synthesis is depressed. The mechanism of inhibition will be investigated by examining host cell DNA by centrifugation techniques to determine whether cleavage of host DNA occurs. Also the effect of protein inhibition on host DNA synthesis will be determined. Infected isolated nuclei will be used to investigate RNA and DNA synthesis by isotopic methods, and isolation and characterization of the products will be carried out.