We isolated the chick orthologue of the Idl helix-loop-helix gene and analyzed its expression pattern during early chick embryo development by whole-mount in situ hybridization. The Idl expression pattern is dynamic and confined to discrete locations including the neural plate border. prospective olfactory placode, hindbrain, mesenchyme of distal branchial arches and adjacent to placodes, and the distal mesoderm of the limb buds. (C) 2001 Elsevier Science Ltd. All rights reserved.