The ubiquitin proteasome system plays an important role in the pathophysiology of Multiple Myeloma, highlighted by the unique success of proteasome inhibitors in this malignancy. Using topic-defined microarrays we have looked at expression of ubiquitin proteasome system genes in 2 multiple myeloma cell lines and normal bone marrow samples. Overall design: Normal bone marrow samples from 5 healthy donors and 2 multiple myeloma cell lines, OPM-2 (4 replicates) and U266 (3 replicates), were included in the study.