We have adapted a fluorescence in situ hybridization (FISH) method to detect nascent RNA molecules of the imprinted SNRPN gene at the initial transcription sites in nuclei of human HL60 and WI38 cells. Simultaneous detection of RNA and DNA of SNRPN by FISH using the cosmid probe confirmed its monoallelic expression in these cell lines. Treatment of both cells by inhibitors of DNA methylation and histone deacetylation resulted in time-dependent increase of the cell population with the biallelic expression of SNRPN.