Ten specific pathogen-free cockerels aged 8-12 months were infected by ocular instillation of 2 x 10(7) embryo-lethal doses 50% of a virulent viscerotropic strain of Newcastle disease virus (Fontana 1083 strain). The birds were killed at 24-h intervals after infection and tissues were collected for histological and immunohistochemical evaluation. The infection ran an acute course, severe clinical disease occurring within 72 h of infection. By gross and histological examination, the most severe damage detected was found to occur in lymphoid areas in a number of tissues. The greatest amounts of viral antigen detected occurred in the proventriculus, small intestine, spleen, thymus and eyelid. Immunohistochemical labelling was confined to large mononuclear cells.