Monitoring patients with multiple myeloma during and after treatment for the presence of residual myeloma cells (minimal residual disease - MRD) has been shown to give a major insight into the effectiveness of treatment. It has been reported that Wilms' tumor gene (WT1) expression levels measured by real-time quantitative polymerase chain reaction was useful as an indicator of minimal residual disease in leukemia and myelodysplastic syndrome. The aim of this study was to measure levels of WT1 expression, in order to find a possible association between the expression of this gene and multiple myeloma at diagnosis. If an association was found, the WT1 gene could be evaluated as an MRD marker by comparison with other prognostic factors. We investigated peripheral blood WT1 expression level measured by real-time light cycler quantitative polymerase chain reaction in 50 newly diagnosed multiple myeloma patients. The normal WT1 gene copy number was found to be <23/microl cDNA and all patients with myeloma were found to have normal WT1-mRNA levels. On this basis WT1 expression analyses is unlikely to be a useful genetic marker for routine clinical use in multiple myeloma patients at diagnosis.