RT-PCR with patient-specific primers detects clonotypic transcripts from both blood and BM of the relevant patient but not from unrelated patients or healthy donors. One microgram of total RNA isolated from myeloma and control BM and PBMC was reverse transcribed and amplified with patient-specific primers. A clonal product was detected only in BM and PBMC of the patient for whom the primers were generated. The following primer pairs were used in PCR: (A) consensus IgH VDJ, (B) histone (housekeeping gene), (C) primers for CDR2/CDR3 of patient 10, (D) primers for CDR2/CDR3 of patient 11, (E) primers for CDR2/CDR3 of patient 12. Lanes 1 and 2, unrelated myeloma patient; lane 3 patient 10 BM; lane 4, patient 10 PBMC; lane 5, patient 11 BM; lane 6, patient 11 PBMC; lane 7, patient #12 BM; lane 8, patient 12 PBMC; lanes 9 and 10 healthy control BM; lane 11 healthy control PBMC; lane 12 water control.