The nasal washings from 52 volunteers were tested. Twelve had received a partly attenuated A2 influenza Leningrad/4/65 and 37 a similar B England/101/ 62 strain. Interferon was detected by titration with rhinovirus type 2 in human fibroblasts and with Sindbis virus in a continuous line (V 3) of monkey kidney cells. In volunteers given influenza B, interferon was found in specimens collected 4 days after inoculation in 12 of 22 infected volunteers and 2 of 15 uninfected volunteers. There was no relation between the presence of interferon in infected volunteers and the clinical severity of illness but volunteers who developed higher titres of antibody in convalescence had had higher peak interferon titres in the acute phase of the illness than those who developed low titres.

HUMAN erythrocytes suspended in glucose buffered at about pH 5–5.8 may aggregate and this aggregation can be detected by the rapid settling of cells in a tube or by the pattern of deposit in a tube or plastic haemagglutination plate. The haemaggregation is inhibited by sodium chloride and quite specifically by polioviruses, by influenza viruses1 and by other biologically active substances including nucleic acids, mucoproteins, tuberculin and rhinoviruses2. Old tuberculin and purified protein (derivative) inhibit the haemaggregation of untreated erythrocytes, but certain viruses inhibit only erythrocytes treated with trypsin. The inhibition caused by tuberculin is correlated with skin sensitizing activity and is inhibited by specific antibody3,4.