Objective To study the expression of Id mRNA in hematologic malignant tumor cells.Methods The total cellular RNA were extracted from peripheral blood mononuclear cell(PBMC) of the patients with hematologic disorders and health adults as well as from four tumor cell lines(Daudi,Jurkat,K562,U937).The primers based on the reported sequences of Id1,Id2 and Id3 were synthesized.The mRNA expression levels of Id1-Id3 in PBMCs and tumor cells were detected by RT-PCR.Results The mRNA expression of Id1,Id2 and Id3 showed different levels in different cells.Id2 was widely expressed in both normal and malignant cells as well as many types of lymphocyte.The expression levels of Id1 and Id3 mRNA in tumor cells and PBMC from hematologic disorder patients were significantly higher than those in PBMC of healthy adults.Conclusion Different Id genes have different expression patterns in different cell types.It seems that Id1 and Id3 may play some important roles in the proliferation and differentiation of lymphocytes and in the development and growth of tumors.