A member of the genus Paramyxovirus of the family Paramyxoviridae which is associated with a variety of respiratory illnesses. The virus particles range in size from 90 to 200 nanometers, agglutinate red blood cells, and (like the influenza viruses) contain a receptor-destroying enzyme. They differ from the influenza viruses in their large size, their possession of the larger ribonucleoprotein helix characteristic of the paramyxoviruses, their tendency to lyse as well as agglutinate erythrocytes, and their generally poor growth in eggs. In culture these viruses grow well in primary monkey or human epithelial cells; although they produce little cytopathic effect in the culture cells, they are easily recognized by the hemadsorption method. They are relatively unstable upon storage, even at freezing temperatures. Laboratory diagnosis may be made by hemagglutination-inhibition, complement fixation, and neutralization tests of the patient's blood.