The detection of the two subtypes of BCR-ABL tran­scripts, b2/a2 and b3/a2, was performed by reverse transcriptase-polymerase chain reaction (RT-PCR) on total RNA extracted from bone marrow and peripheral blood samples. Total cellular RNA was extracted by the method of Chomczynski and Sacchi [15]. Complementary DNA (cDNA) was synthesized using random hexamers and the GeneAmp RNA/PCR kit (Perkin Elmer Cetus, Norwalk, CT, USA), following the recommendations of the manufacturer. The following primers were used: con­sensus ABL 3 (5’-CCG CTG CTC AGC AGA TAC TC-3’), BCR 1 (5’-TGC AGA GTG GAG GGA GAA CAT-3’) and ABL 4 (5’-CTT CTC GCT GGA CCC AGT GA-3’). PCR was performed in a DNA Thermal cycler 2400 (Perkin Elmer Cetus) under the following conditions: 1 min. at 95°C, 1 min. at 65°C, 90 seconds at 72°C, for a total of 45 cycles. The PCR products were visualized after electrophoresis on 2% agarose gels with ethidium bromide and UV illumination. The size of the obtained fragments was 496 and 571 bp, respectively, for the b2/a2 and b3/a2 transcript, and 260 bp for the control ABL product.