We studied the expression of mouse HES-6, a new member of the Hairy/Enhancer of split family of basic helix-loop-helix transcription factors. HES-6 is expressed in all neurogenic placodes and their derivatives and in the brain, where it is patterned along both the anteroposterior and dorsoventral axes. HES-6 is also expressed in the trunk, in the dorsal root ganglia and in the myotomes. In the limb buds HES-6 is expressed in skeletal muscle and presumptive tendons. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.