Modern treatment protocols lead to complete remission in a high proportion of patients with childhood acute lymphoblastic leukemia (ALL). However, a large number of them show a relapse of the disease. Treatment failure in these patients is mainly attributable to de novo or acquired resistance to a wide variety of cytotoxic drugs, which is called multi drug resistance (MDR). Expression of multi drug resistance 1 gene (MDR1) is implicated in the drug-resistance mechanism. In order to contribute further information we present a rare case of a 15-month old girl with newly diagnosed CALLA positive pre-B acute lymphoblastic leukemia with favourable prognostic factors at diagnosis who experienced a relapse of the disease. Using reverse transcriptase polymerase chain reaction method, m-RNA expression of the MDR1 gene upon relapse, was five-fold compared with that at diagnosis. This is the first report on increased mRNA expression at relapse in a paired sample of a child with ALL in our region.