Our interest in isolating the gene(s) for ataxia-telangiectasia has prompted us to construct a physical map of chromosome 11q22.3 using markers localized to this region by linkage analysis and/or hybrid cell panels. Twenty-two markers have been analyzed by pulsed-field gel electrophoresis. Nine of these markers form an approximately 2-Mb long-range contiguous map. An average distance of 200 kb between probes in this map should facilitate the isolation of new cDNAs, anonymous probes, and YACs in an orderly way.