The interphase nucleus of a cell is organized into non-random, cell-type specific chromosome territolies (CTs). In lymphocytes, a gene-density correlated radial arrangement has been identified, with gene-dense CTs located more in the nuclear interior and gene-poor CTs located towards the periphery. However, other factors such as chromosome size, transcription and interactions of the nuclear membrane and matrix are also involved in the final ammgement of CTs within a nucleus. In this project, the CTs of chromosome 11 and X were studied in five different cell types of mouse B cell lineage: diploid preB cells, primary B cells of [T38HxBALB/c]N wild-type mice, primary B cells of [T38HxBALB/c]N with rcpT(X;l1) mice, primary B cells of BALB/c mice and a Wehi 231 mouse B lymphoma line. These two chromosomes have not been studied before in the mouse. 3D FISH experiments that labeled the CTs of chromosome 11 and X with chromosome-specific paints were carried out for each cell type. The karyotype regarding these two chromosomes and specificity of the chromosome paints was first confim1ed through 2D FISH experiments. The radial distance from the centre of each CT to the centre of the nucleus was measured lIsing AxioVision 4.8 software. The results show a non-random, statistically significant and cell-type specific nuclear distribution of these two chromosomes. Altered nuclear positions of translocation chromosomes in normal healthy mice and as a result of tumorigenesis were observed in the primary B cells of [T38HxBALB/c]N with rcpT(X;l1) mice and in the Wehi 231 mouse B lymphoma line, respectively.