In order to determine the involvement of CALM-AF10 fusion transcripted in primary leukaemias with t(10;11) and its chemotherapy sensitivity in vitro, the AF10-CALM fusion transcripts were detected by reverse transcription-polymerase chain reaction (RT-PCR), and the chemotherapy sensitivity testing in vitro was undergone by MTT assay in five t(10;11) leukemia samples from patients with ALL, AML and lymphoblastic lymphoma. The results showed that five different-sized AF10-CALM product and four different-sized CALM-AF10 products were detected. The chemotherapy sensitivity of leukemic cells with t(10;11) in vitro to drugs is lower than that of leukemic cells without t(10;11). 3 out of 5 cases of t(10;11) leukemia were sensitive to chemotherapeutic drugs, while 31 out of 36 cases of leukemia without t(10;11) were sensitive at same condition. There were significant differences (P < 0.01), consistent with clinical features of patients. Apoptosis rate of leukemic cells with t(10;11) induced by chemotherapeutic drugs was lower than that of leukemic cells without t(10;11), (16.37 +/- 2.56)%, and (33.75 +/- 5.59)%, respectively (P < 0.01). It is concluded that the CALM-AF10 fusion transcripts are a common features and are involved in the pathogenesis of haematological malignancies with t(10;11), and are associated with a poor prognosis.