Genomic imprinting is the phenomenon by which one of the two alleles of certain genes are preferentially expressed according to their parental origin. Imprinted genes are involved in normal embryonic growth and behavioral development. Consequently, relaxation or loss of monoallelic expression of these genes results in numerous human hereditary disorders as well as tumorigenesis. However, despite suggestive evidence, it has not been clarified if the expression status of imprinted genes and their allelic expression patterns varies within the normal populations. In the present study, we collected peripheral blood leukocyte samples from 262 normal individuals in 68 families and analyzed for the expression status of IGF2, SNRPN and IMPT1 genes by using a quantitative RT-PCR method. By RFLP analysis, the parental origin could be determined for 38 cases for IGF2, 36 cases for SNRPN and 34 cases for IMPT1. Whereas in all cases the SNRPN gene was expressed exclusively from the paternal allele, paternal allele-specific expression of IGF2 was relaxed in some cases. In most of cases maternal allele-specific expression of IMPT1 was relaxed and each individuals exhibited distinct allelic expression bias. Our findings show that certain imprinted genes are involved in epigenetic heterogeneity as visualized by variable allelic expression patterns in normal human population. There might be a possibility that a part of individuality is influenced or determined by epigenetic heterogeneity.