The chromosomal translocation t(1;19)(q23;p13) and its variant form der(19)t(1;19) found in 3-5% of acute lymphoblastic leukemia (ALL) results in the expression of the E2A-PBX1 fusion transcript. Although strongly associated with a pre-B immunophenotype, we report the occurrence of t(1;19) in bone marrow or peripheral blood in nine patients with ALL with the following immunophenotypes: pre-B ALL (four), c-ALL (two), c-ALL clg not tested (one), null-ALL (one) and mature B-ALL (one). The E2A-PBX1 fusion transcript investigated by reverse-transcriptase polymerase chain reaction (RT-PCR) was seen in all patients at diagnosis and/or on follow-up samples. Six patients are alive in first clinical remission. Of these patients, three were PCR+ve from between 2 and 38 months from diagnosis, and three were PCR-ve when examined at 5, 26 and 51 months from diagnosis. Two patients are in second remission. One was PCR+ve at 18 months, suffered a CNS relapse at 21 months but was PCR-ve 1 month later. The other was PCR+ve in remission at 2 and 11 months from diagnosis and in testicular relapse at 31 months, but was PCR-ve 5 months later. The remaining patient died 2 months from diagnosis and was not investigated in remission. The prognostic significance of these findings remains to be investigated.