By using a map of the unique region of DNA encoding the fur small heat-shock proteins of Drosophila melanogaster (hsp 22, hsp 23, hsp 26, and hsp 28), and a simple mapping technique, the positions of the DNase I hypersensitive sites of chromatin in the vicinity of these genes have now been determined. The major chromatin-specific sites occur at the 5' ends of each of the four heat-shock protein genes in embryo nuclei. These genes are not active in the nuclei analyzed but can be quickly induced in these cells by the heat-shock stimulus. The chromatin structure indicated by DNase I hypersensitivity may be a necessary factor in the general mechanism of gene activation.