The MLL gene breakpoint-cluster region (BCR) is a known hot-spot for chromosomal translocations in human leukemias. We mapped core histone modifications and histone H1 along the MLL gene in Jurkat cells and human CD34(+) progenitor blood cells by chromatin immunoprecipitation. Within the BCR, we found specific histone patterns that were different from other genomic regions and a histone H1-free fragment at the telomeric end. Core histone acetylase/deacetylase activities were also found within the BCR. In the studied cell models, chromatin components at the MLL BCR suggest an asymmetric organization that may influence early molecular events eventually leading to chromosomal translocations.