During two epidemics of acute diarrhoea in China in late 1982/early 1983, more than 12 000 adults in two coal mining districts were affected. The virus isolated from stool samples resembled a rotavirus morphologically. Antigenically it lacked the group antigen shared by known rotaviruses. Like other rotaviruses it had a double-stranded RNA with 11 discrete segments, but the pattern of migration of the segments on polyacrylamide electrophoresis differed from those of other rotaviruses.