An effort was made not to exceed passage 72. Cultures of primary AGMK were purchased from MA Bioproducts. Viruses. Rotaviruses for primary isolation were in the form of diarrheal or normal feces, either as approximate 10%o suspensions or as rectal swab fluids. Seventy-three such fecal samples containing rotavirus were kindly supplied by the following investigators: H. W. Kim and colleagues, Children'

The authors are indebted to Mrs. Erminie B. Compton and Miss Carol L. Voss for assistance in compilation of data.* Subsequent to the submission of this manuscript for publication the term "coronavirus" was proposed to include the avian infectious bronchitis virus (IBV) group, the mouse heaptitis virus (MHV) group, and the human "avian IBVlike" virus group (Coronaviruses, Nature 220: 650, 1968).

An immune adherence hemagglutination assay (IAHA) and a modified enzyme-linked immunosorbent assay for antigenic characterization of human rotaviruses were developed. The designations of type 1 and type 2 were identical to those established previously by specific complement fixation, enzyme-linked immunosorbent assay, and immune electron microscopy. By IAHA (and modified enzyme-linked immunosorbent assay) certain animal rotaviruses were found to be closely related to human rotavirus type 1. The pattern of IAHA reactivity and the cell culture neutralization serotype were found to be distinct properties. The separation of neutralization and IAHA reactivity was apparent when animal rotaviruses which were distinguishable from each other by neutralization assays were found to share IAHA specificity. Further evidence for the dissociation of the neutralization and IAHA specificities was found in studies of human and bovine rotaviruses which underwent genetic reassortment during coinfection. Thus, it appeared that the IAHA and neutralization antigens were coded for by different genes. In view of these findings, we suggest that the term serotype be reversed to identify the antigen that reacts with neutralizing antibodies as is customary for other viruses and that the term subgroup (instead of serotype) be used for the specificity detected by specific complement fixation, enzyme-linked immunosorbent assay, and now IAHA.

The possibility of immunizing human infants against rotaviruses, which cause severe dehydrating diarrheal disease, may depend on the use of a related rotavirus, derived from another animal species, as a source of antigen. To test the feasibility of this approach, calves were infected in utero with a bovine rotavirus and challenged with bovine or human type 2 rotavirus shortly after birth. Infection in utero with bovine rotavirus induced resistance to diarrheal disease caused by the human virus as well as the homologous bovine virus. These data suggest that the bovine virus is sufficiently related antigenically to the human type 2 virus to warrant further evaluation of the former as a source of vaccine.