Chronic exposure to high concentrations of benzene is associated with an increased incidence of myelodysplastic syndrome (MDS) and acute myelogenous leukemia (AML). Studies of patients occupationally exposed to benzene show a pattern of cytogenetic aberrations involving loss of all or part of chromosomes 5 and/or 7 as well as trisomy 8 and we have previously reported that hydroquinone (HQ) induces deletions of 5, 7 and 8. Benzene metabolism is a requirement for bone marrow toxicity and the phenolic metabolites, HQ and catechol (CAT), have been implicated in benzene hematotoxicity. A research project was designed to determine whether CAT by itself and in conjunction with HQ could directly induce loss of chromosome 5 and/or 7 and gain of chromosome 8. Using fluorescence in situ hybridization with chromosome-specific 5, 7, and 8 probes we demonstrate that 5 to 150 uM CAT does not produce chromosomal aberrations, however CAT and 25 uM HQ can act in synergy to induce dose dependent loss of these chromosomes. In addition HQ/CAT selectively induces -5q which is not observed for HQ only. These results demonstrate for the first time that CAT/HQ act in synergy to induce specific chromosome loss found in secondary MDS/AML.