Monoclonality on B-cells is well known to be determined on the basis of presence of a rearranged-IgH gene, which is detected by Southern blot hybridization (SBH) remaining to be elucidated in respects of not only time-consumed, labour and cost benefit and also the use of much DNA samples. Alternative to this SBH, we examined the clinical usefulness of monoclonal analysis by the polymerase chain reaction technique which amplifies rearranged-CDR III region of IgH gene (IgH-PCR). The detective sensitivity of the IgH-PCR was different dependently upon each analysis for amplified products, namely 10(-2) per mononuclear cells in agarose gel analysis and 10(-3) in polyacrylamide gel and single strand conformation polymorphism analysis (PAGE and SSCP). Then, using the IgH-PCR and PAGE/SSCP analysis, 75 Japanese patients with B-neoplasm and 23 with T-cell neoplasms were examined for clonal IgH rearrangements. The diagnostic sensitivity in each group of B-ALL, B-CLL, B-lymphoma, HCL, AML with B-cell antigens, and non-T cell neoplasms was 88%, 92.3%, 71.4%, 100%, 57.1%, and 0%, respectively, with an overall sensitivity and specificity of 88% and 100%. This indicates that PCR analysis is very useful in detecting the clonal rearrangement of IgH genes on B-cell neoplasms, especially on ALL and CLL corresponding to neoplasms counterparting to naive B-cells.