Chromatin structure plays a critical role in eukaryotic gene expression. Chromatin immunoprecipitation assay (ChIP) provides a powerful tool to analyze the interaction of trans-acting factors with specific chromatin regions in vivo, as well as the role of histone modifications in gene regulation. A simple ChIP protocol is established and used to study the H3 acetylation pattern of the β-globin locus in MEL cells. DMSO induction results in a dramatic increase in H3 acetylation at hypersensitive site HS2 and active gene (βmaj) promoter, whereas the inactive gene (Ey) promoter maintains low acetylation. This result indicates that the ChIP method is feasible.