Most of the current studies of respiratory diseases of man and animals are aimed at determining their virus etiology, and considerable progress has been made, particularly since the advent of tissue culture methods. The relatively new hemadsorption technique (1) is used extensively in work with many of the respiratory disease viruses. Essentially, this is a system in which red blood cells of various species, depending on the virus, are added to the infected tissue culture tubes. The red blood cells will adhere to the surface of t,he infected cells. Hemadsorption has been used for establishing the identity of isolates as well as isolating the virus from clinical specimens. Hemadsorption is a specific phenomenon which is dependent upon the hemagglutinating properties of the virus. It was first reported in 1957 by Vogel and Shelokov who worked first with the influenza viruses and later extended these studies to certain other members of the myxovirus group. This technique has been used to good advantage in our laboratories. The recovery of parainfluenza 1, 3 (2), and possibly 4 (3) viruses, from children was largely due to the use of hemadsorption because many of the strains of parainfluenza 3, particularly, produced no cell degeneration on original isolation from children, and the virus was detected only by the use of hemadsorption. The first suggestion that a virus recovered from cattle with shipping fever might be a myxovirus resulted from the use of hemadsorption. It was then relatively simple, by using type-specific human parainfluenza 3 antiserum, to demonstrate the relationship of this virus to the human virus (4). When this newly described hemadsorption technique was used in conjunction with monkey kidney tissue cultures, two new myxoviruses were recovered from children with respiratory illnesses (2). One of the viruses, the present parainfluenza 3, was significantly associated with febrile illness during an outbreak of respiratory disease in a nursery. About the same time the present parainfluenza 1 virus was also recovered from children. In a study of 1,738 children in three hospitals in the Washington, D.C., area, one or the other of these two hemadsorption viruses was recovered from 54 (6 percent) of 879 patients with respiratory disease. It appeared that the two viruses were capable of causing a wide variety of clinical manifestations including croup, pneumonia, bronchiolitis, pharyngitis, and mild febrile disease. Table 1 shows the recovery of parainfluenza 1 and 3 viruses from children with various respiratory disease syndromes. Evidence of year-round occurrence of hemadsorption virus infections has been obtained (5). Other recent evidence relative to reinfection of Dr. Abinanti is with the Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, Public Health Service. This paper was presented at the Conference of Public Health Veterinarians, November 2, 1960.