Faecal samples from 238 patients with gastroenteritis were examined by direct electron microscopy using grids with thin carbon film. Of these samples 18 were found to contain Norwalk agent-like particles, calicivirus, astrovirus and parvovirus-like particles. Immune electron microscopy was performed on a serum pair and faeces from one of the patients with astrovirus. An antibody response was demonstrated, suggesting that the virus was the etiological agent of the infection.