Genomic imprinting is an epigenetic mechanism in mammals by means of which the differential expression of certain gene alleles is governed by their parental origin from generation to generation. Epigenetic features such as allelic DNA methylation and chromosome-specific chromatin conformation have been related with imprinting. We have analyzed modifications of methylation in the maternally imprinted U2af1-rs1 gene in three stages of male germ cell line development. Our results showed that restriction sequences analyzed were completely unmethylated in primordial germ cells, which are pluripotential cells that are the origin of germ cell line development, (PGCs) of the EG-3 cell line and the methylation status increased progressively in stem spermatogonia. and mature sperm cells. We also studied the chromatin organization of the U2af1-rs1 imprinted gene in EG cells and stem spermatogonia cells. This analysis revealed that the chromatin region analyzed was more sensitive to DNase-I in male germ cell nuclei than in Sertoli cell nuclei.