Summary: An “intersecting serum scheme” for the identification of viral isolates by testing against pools of type-specific ECHO virus immune sera is described. Each specific serum is included in two pools and identification is made by demonstrating neutralization of the agent by the two pools sharing a common immune serum. The identification of all ECHO virus isolates tested in this scheme agreed with that made in tests with individual immune sera. The ECHO virus immune serum pools did not neutralize isolates of the poliomyelitis and Coxsackie viruses. A single cell culture tube may be used for each immune serum pool-virus mixture.