The cores of human and simian immunodeficiency viruses (HIV and SIV) were observed by negative staining after isolation of the core with Nonidet P40 and glutaraldehyde. Four kinds of cores were found: asymmetric and symmetric sectoral shapes, a bar shape, and a triangular shape. These results were confirmed by the examination of ultrathin sections of whole virions. In some virions, the connection between the core and the envelope was observed after freeze fracturing. Its structure was considered to be characteristic of an intermediate stage of viral maturation. The HIV-1 core was reacted with anti-HIV-1 p24 mouse monoclonal antibody.

Within 10 minutes after tritium-labeled adult T-cell leukemia-associated virus (ATLV) inoculation, silver grains were found over human lymphocytes. At the time of entry of ATLV, the viral envelope was observed to fuse with the cell membrane.

A method for removing inhibitor(s) of the PCR assay for the direct detection of cholera toxin A gene (ctxA) in human faeces is described. Inhibitors of the PCR were removed by centrifugation and the activity of the remaining inhibitors by dilution. Based on these data, a protocol was developed for pre-treatment of stool specimens for PCR assay, and a simple and rapid protocol was constructed for the diagnostic detection of the ctxA genes in stool specimens in combination with single band detection on gel electrophoresis, dot-blot hybridisation and enrichment culture. This protocol was applied to clinical specimens and showed that the PCR method gave 100% agreement with established culture methods for the detection of cholera toxin-producing Vibrio cholerae 0 1 . This protocol was considered to be useful because of its simplicity and the rapidity of diagnosis.

HIV particles were usually seen on the surface of established lymphoid cells derived from AIDS patients or on CEM cells infected with HIV, and sometimes in cytoplasmic vacuoles. The virus particles were formed by a budding process from the plasma membrane of an infected cell. The budding particles were of a doughnut form. Various profiles of virus particles were seen extracellularly: type 1 had a bar-shaped, electron-dense core, type 2 had a central and type 3 an eccentric electron-dense round core, type 4 was doughnut-shaped, and type 5 had a layered core. However, projection patterns of the AIDS virus model suggested that type 1, 2 and 3 particles are similar. Therefore, the AIDS virus may be one of three main types: with or without a dense core, and with a layered core. It is thought that a particle with a layered core and a doughnut-type particle may be immature viruses.