Chromatin in the 5' flanking region of the transcriptionally active chicken adult beta(beta A) globin gene is hypersensitive to nuclease digestion. When plasmids carrying this gene are combined with histones in the presence of extracts from 9-day-old chicken erythrocyte nuclei, the resultant complex displays hypersensitive behavior in the same region. No such behavior is observed with extracts from cells in which the beta A-globin gene is not expressed. Partially purified preparations of the factor conferring hypersensitivity bind preferentially to DNA fragments containing the hypersensitive region.