We describe the polymerase chain reaction (PCR) method using stained bone marrow smears as sources of RNA. The amount of extractable RNA decreased during the process of making and staining bone marrow smears. The sensitivity of the reverse transcriptase-based polymerase chain reaction (RT-PCR) method for detecting target mRNA-positive cells in 5 x 10(5) suspended cells and stained bone marrow smears were 1:10(5) and 1:5000, when we used K562 cells. The bone marrow smears of 21 patients with chronic myelogenous leukemia (CML) were examined using this method. We extracted RNA from stained specimens stored at room temperature for 5-14 years. Twelve of 21 (57%) smears showed positive results for bcr/abl. The carrier RNA improved the recovery when added at the step of RNA extraction. These data indicate that mRNA is present in stained bone marrow smears for at least 14 years and that the sensitivity of RT-PCR is adequate for molecular analysis.