PCR analysis to detect Igκ transcripts in L1236 cells as well as in H-RS cells of the patient’s affected bone marrow. Lane 1, L1236, DNA; lane 2, L1236 cDNA; lane 3, section of the patient’s affected bone marrow, cDNA; lane 4, no template; lane 5, 100-bp ladder. Using an oligonucleotide hybridizing to the V_κ leader sequence and an oligonucleotide hybridizing to the CDRIII of the rearranged V_κ genes, a specific product was amplified from DNA as well as cDNA. The products differ in length due to splicing of the leader intron. V_κ transcripts were amplified and sequenced from L1236 cells as well as from the bone marrow section. The cDNA of the bone marrow section showed a slight contamination with DNA, resulting in an additional band.