Dr. Eastmond and colleagures at the University of California, Riverside investigated whether chromosomal changes could be used as biomarkers of benzene exposure in mice and humans. The first part of the study involved detecting chromosomal alterations in cells using a modification of a molecular cytogenetic technique known as fluorescence in situ hybridization (FISH). Eastmond and colleagues evaluated the frequency of such chromosomal aberrations in the erythrocytes (red blood cells) from the bone marrow of mice exposed to various doses of benzene and for different exposure durations. The investigators also tested aberrations in chromosomes 1 and 9 of peripheral blood cells from groups of Chinese and Estonian workers occupationally exposed to benzene. The second part of Eastmond's proposal was to determine whether benzene or its metabolites affect DNA indirectly, acting through the nuclear enzyme topoisomerase II. This enzyme plays a key role in maintaining the chromosomal structure, so inhibiting topoisomerase II function might lead to chromosomal damage or to the development of aberrations.