In an attempt to define the clinical utility of immunoglobulin heavy chain (IgH) gene rearrangement identification for tumour cell detection in multiple myeloma, we investigated 36 consecutive newly diagnosed patients intended for high-dose chemotherapy in a study protocol. After identification of the IgH rearrangement, an allele specific oligonucleotide (ASO) was constructed and used in a semiquantative PCR for minimal residual disease (MRD) evaluation. The myeloma-specific IgH gene rearrangement could be identified and an ASO primer constructed in 24 (67%) of the patients. All of these patients underwent transplantation; 22 were autologous, of whom three had PCR-negative stem cell harvests, and two were allogeneic. 10 patients achieved a clinical complete response (CR) and five were PCR negative in sequential bone marrow analyses. In patients not achieving CR, PCR negativity was occasionally found, but in general the PCR results reflected the clinical status of the patients. No consistent relationship between the bone marrow MRD status and the clinical course was found, and early relapses occurred also in PCR-negative patients.