Acute myeloid leukaemias (AML) arising in irradiated CBA/H mice frequently have breakpoints in the F region of chromosome 2. The closely linked cytokine genes interleukin (IL)-1 alpha and beta map to this region, and the beta gene is deregulated in some AMLs. Using pulsed-field gel electrophoresis techniques, we show here that an 800 kb 2F region encoding IL-1 alpha and beta is not obviously rearranged in six leukaemias carrying chromosome 2 abnormalities. However, changes in IL-1 region DNA methylation in three leukaemias may be consistent with loss of hypermethylated sequences from one chromosome copy. These possible 2F region losses are discussed in relation to genomic imprinting and its potential role in murine myeloid leukaemogenesis.