Résumé : To determine the relative importance of two known serotypes of human rotavirus, we developed an enzyme-linked immunosorbent assay to differentiate serotype-specific rotavirus antigen and antibody. Using this technic, we studied the epidemiology of the two serotypes in acute gastroenteritis. Seventy-seven per cent of 414 rotavirus isolates were Type 2, and the remainder were Type 1. The serotype distribution was similar in specimens from children in Washington D.C., and other parts of the world. Seroepidemiologic studies revealed that most children living in the Washington, D.C., area acquired antibody to both types by the age of two years. An analysis of children who were reinfected indicated that sequential infections usually involved different serotypes and that illness caused by one serotype did not provide resistance to illness caused by the other serotype. These results suggest that, to be completely effective, a vaccine must provide resistance to both serotypes. (N Engl J Med 299:1156–1161, 1978) ROTAVIRUS is an important cause of gastroenteritis of infants and children in many parts of the world.12 Because the virus does not grow efficiently in tissue culture, conventional neutralization methods cannot be used to examine its serotypic variations.34 Recently, two human rotavirus serotypes were distinguished by complement fixation,5 immune electron microscopy5 and immunofluorescence.6 The latter two methods are not practical for serotyping of large numbers of rotavirus-positive specimens whereas complement fixation is not sensitive enough for use with low-titered preparations. We recently described the technic of enzyme-linked immunosorbent assay for the detection of rotavirus antigen and antibody.7 8 9 10 This assay is. © 1978, Massachusetts Medical Society. All rights reserved.