DCC (deleted in colorectal cancer) is a candidate tumor suppressor gene recently identified on chromosome band 18q21. Loss of one DCC allele or decreased DCC expression occurs in more than 70% of colorectal cancers, suggesting that DCC inactivation constitutes a critical event in the development of these tumors. Using polymerase chain reaction amplification of cDNA, we have studied DCC expression in bone marrow from 4 patients with leukemia (1 chronic myeloid leukemia-blastic crisis, case 1; 1 acute myeloid leukemia, case 2; 1 T-cell acute lymphoblastic leukemia [ALL], case 3; 1 B-cell ALL, case 4) showing loss of one DCC allele due to monosomy 18. We also studied DCC expression in multiple control samples, including normal lymphocytes, normal tonsillar tissue, and leukemias without 18q abnormalities. Four primer pairs consistently amplified the predicted DCC sequences from cDNA prepared from all control samples. However, in samples with monosomy 18, DCC transcripts were either not detected (case 1) or detected at a very low level (cases 2, 3, and 4). Southern analysis showed no structural rearrangement of the remaining DCC locus in all leukemia samples. Thus, loss of DCC expression was demonstrated in association with loss of one DCC allele in all cases tested. These results suggest that, as for colorectal tumors, the inactivation of DCC can have a role in the development of hematologic malignancies.