Indirect immunofluorescence staining with human anti-centromere autoantibodies from a patient (LU 851) suffering from the CREST form of scleroderma was used to analyse chromosome topology in interphase nuclei of rat-kangaroo (PTO) and Indian muntjac (IM) cells. In some cells, centromeres were arranged in pairs suggesting association of homologous chromosomes. Clustering of centromeres at one pole of the nucleus (Rabl configuration) and other patterns suggesting higher order organization were also observed. In one fifth of the IM cells it was possible to identify the intranuclear location of each single chromosome on the basis of the morphology of the immunostained centromeres. In 30% of the IM cells in which centromeres could be identified, homologous chromosomes occupied adjacent territories within the interphase chromatin.