Four cytopathic agents were isolated in the test group, two of which were readily subcultured for at least three successive passages.

Three cytopathic agents were recovered in the control group, two of which have been identified as adenovirus type 5 and adenovirus type 3. The unidentified agents tested so far are sensitive to ether and to pH 3. The results of acridine-orange staining and the immunofluorescence technique, using a conjugated control serum and two conjugated convalescent infectious mononucleosis sera, indicate that the isolated agent or agents in the test group are RNA-type agents with a cytoplasmic cycle of development. The overall results of this study lead the authors to suspect a respiratory syncytial-like myxovirus as the as yet unidentified agent which they recovered.