The 14q+ chromosomal anomaly commonly found in cases of lymphoid neoplasm recurrently occurred during the lymphoid crisis of a patient with Philadelphia chromosome (Ph) positive chronic myelogenous leukemia (CML). At presentation lymphoblasts, with pre-B phenotype increased, and both the Ph and 14q+ were found in the same metaphases. After treatment with vincristine and prednisolone, the patient entered into the chronic phase, and only a Ph was detected in 100% of the cells examined. The 14q+ reappeared at the recurrence of the lymphoid crisis, and then disappeared in the second chronic phase. The BCR/ABL mRNA, which is specific for CML, was detected in the blastic cells by a method using reverse transcriptase and polymerase chain reaction. The rearrangement of the immunoglobulin heavy chain gene (JH gene) was also detected in the blastic cells. These results suggest that the 14q+ was closely associated with the lymphoid crisis of the CML patient.