Representative RT-PCR screening for p190 BCR-ABL transcripts in leukocytes from a healthy adult. The ethidium-bromide–stained agarose gels show quadruplicate PCRs (labeled a, b, c, and d) for each cDNA aliquot (labeled 1 through 10) including 1 of the 4 negative (Neg.) controls and 1 positive (P) control specimen (SD1 cell line). The first lane on each gel is a 123-bp DNA ladder marker.