WITHIN the enterovirus group of Picornaviruses, 63 serotypes have been recognized (1-3). Since numerous untypable strains are still being isolated in laboratories throughout the world, many new types may be awaiting description and official recognition. For diagnostic laboratories which routinely perform virus isolation tests, the difficult and time-consuming task of typing large numbers of enterovirus strains may discourage detailed study of this important group of disease agents. Attempts to simplify the task of enterovirus identification have led to a number of new techniques and modifications or adaptations of older methods which may help to reduce time and expense. Various antiserum pools have been proposed (4, 5) as a means of decreasing the number of neutralization tests that must be performed, and pooling is practiced routinely in our laboratory at the Communicable Disease Center. A number of enteroviruses cause hemagglutination of human erythrocytes, and these viruses can be typed by hemagglutination-inhibition. This technique has resulted in considerable saving in our laboratory (6). The complement fixation test also has been adapted to the identification of enterovirus isolates. At the Communicable Disease Center this test has often proved useful for typing ECHO type 4 strains, which are difficult to detect by the standard tube neutralization test, and for typing polioviruses in studies of oral vaccine (7). The preparation and standardization of typing antiserums for the Coxsackie group B types is now underway at CDC. The recent work of Dr. Hsiung (8) suggested a simple technique for preliminary grouping of enterovirus isolates which may reduce significantly the number of neutralization tests otherwise necessary. Dr. Hsiung showed that the enteroviruses ordinarily isolated in rhesus monkey kidney cell (RMKC) tissue cultures (all three types of poliovirus, all six types of Coxsackie group B and type 9 of group A, and ECHO types 1 to 27) can be grouped according to the comparative susceptibility of rhesus and patas monkey kidney cells, primary human amnion (HAm) cells, and HEp-2 cells, a line derived from a human carcinoma. Patas kidney cells are not readily available, and the virus types which cause a cytopathic effect (CPE) in tissue cultures of this species include some infrequently encountered ECHO viruses as well as the ubiquitous polioviruses and Coxsackie group B types. HAm cells have a range of sensitivity almost as broad as that of RMKC cells, and in HAm cells some virus types produce CPE inconsistently. HEp-2 cells, however, proved "highly sensitive to the three types of polioviruses and to all six types of Coxsackie B viruses. In recent tests, none of the ECHO virus types produced CPE in HEp2 cells" (8). HEp-2 cells seemed to have characteristics which might prove useful in the routine identification of these viruses. Dr. Hsiung has employed the HEp-2 cell line in studies of field isolates (primary isolates of naturally occurring strains), but her published data include only results of tests with prototype strains. To determine the general HEp-2 cytopathogenicity of enterovirus types, taking into consideration strain variations within each type, all RMKC isolates made in our laboratory during the past year have been tested in HEp-2 cells. We hoped thereby to discover whether passage into tissue cultures of the HEp-2 cell Mr. Marchetti is a public health laboratory technologist and Dr. Gelfand is chief, Enterovirus Unit, Communicable Disease Center, Public Health Service, Atlanta, Ga.