A cold-recombinant virus CR 22, was derived from an attenuated cold-adapted parent strain. A/Ann Arbor/6/60 (H2N2), and a wild-type parent strain, A/Victoria/3/75 (H3N2). Antigenic analysis showed that CR 22 possesses the hemagglutinin and neruaminidase surface antigens derived from the A/Victoria/3/75 (H3N2) parent. From studies of virus-induced polypeptides using polyacrylamide gel electrophoresis, it was deduced that a polymerase protein, P1, is coded and by an RNA segment derived from the wild-type parent; all other genetic elements are derived from the attenuated parent. The attenuated parent and the recombinant CR 22 both possess temperature-sensitive (ts) lesions, evident by restriction of multiplication in fertile chicken eggs or in Madin-Darby canine kidney cell cultures at greater than or equal to 38 C. Genetic analysis of CR 22 by complementation tests using Hong Kong and Wilson Smith neurotropic ts mutants gave evidence for a ts lesion in the genetic elements coding for complementary RNA.