Bone marrow (BM) biopsies occasionally fail to yield aspirate specimens; such "dry taps" pose diagnostic difficulties. In the absence of a BM aspirate, morphological evaluation and cytochemistry rely on core biopsy imprint preparations (IP) and other analyses, e.g., molecular pathology studies, become impossible. The use of imprint preparations (IPs) for molecular diagnostics based on messenger ribonucleic acid (mRNA) analysis by reverse transcription-polymerase chain reaction (RT-PCR) for detection of breakpoint cluster region (bcr) gene rearrangements in chronic myelogenous leukemia (CML) and myeloperoxidase (MPO) mRNA in acute leukemias (AL) is described. Fifteen IPs from five core biopsies (three CML and two AL) were used. Analysis of bcr was positive in all nine IPs from the three cases of CML and was confirmed on peripheral blood samples. Detection of MPO mRNA established the myeloid lineage of the blasts in two cases of AL, when cytochemistry and flow cytometry failed to reveal myeloid markers. These tests are useful when fresh BM aspirate is unobtainable, since multiple imprints of the biopsy are easily prepared at the bedside.