The malignant plasma cells of multiple myeloma (MM) have a low proliferative activity and therefore cytogenetic studies of the disease have been severely limited. We evaluated the role of fluorescence in situ hybridization (FISH) in the detection of numerical chromosomal abnormalities in early stages of myeloma and the applicability of the method to stored archival slides. Old air-dried bone marrow smears from 15 myeloma patients obtained at presentation were probed with alpha satellite DNA sequences to chromosomes 3 and 7. Numerical chromosome aberrations were found in eight (53%) of the patients, including six (of 12) with trisomy 7, and two (of eight) with trisomy 3. This study demonstrates that FISH is a sensitive method for the detection of numerical aberrations in myeloma and for the study of old slides for retrospective analysis.