Human caliciviruses have been reported to be associated with both epidemics of acute diarrhoeal illness and with sporadic cases of gastroenteritis in children. In this study, we report the identification of genogroup II small round-structured viruses or human caliciviruses associated with an outbreak of winter vomiting disease in South Africa. The virus was initially identified by electron microscopic examination of the stools and then further characterised by recombinant immunoassay with expressed capsid proteins to human caliciviruses from genogroups I and II. Both antigenically by the EIA and by sequence analysis of a region of the RNA-dependent RNA polymerase gene, the virus was shown to belong to genogroup II of the human Caliciviridae.