A new virus, found earlier in cultured cells from a nasopharyngeal carcinoma, has been characterized further both biologically and morphologically. Immunologic tests showed that antisera to each of the morphologically similar known animal syncytial viruses failed to neutralize the virus; this demonstrated that the latter is immunologically distinct. Experiments with 5-bromo-2′deoxyuridine indicated that the virus probably possesses reverse transcriptase. The findings are discussed in relation to the animal syncytial viruses which, with the present agent, are considered to form a unique group. It is suggested that this group be designated Echino viruses because of the long spines covering the mature particles.