Strain ME of mumps grown in chick amniotic cavity and purified by differential centrifugation combined with sucrose gradient centrifugation. The structural polypeptides of purified virion were analyzed by SDS polyacrylamide gel electrophoresis. Eleven polypeptides were found. Their molecular weight were between 35K-72K dalton. In addition polymers of HN protein and F1 the large subunit of F protein were detected. Hela, Vero and CE cells were infected with ME strain of mumps virus. The CE cell reveals the most sensitive host cell. CE cell infected with mumps virus and labeled with [35S]-Met, SDS-PAGE and examined by autoradiography. It was found at least eight polypeptides were synthesis in host cells and their molecular weight were between 26.5K to 94K dalton. The time course of the synthesis of polypeptides in the cells were studies. Palse-Chase experiments demonstrated the posttranslational process of Fo----F.