Current knowledge of genes that regulate pattern formation and differentiation processes during mammalian embryonic development is limited. In an effort to isolate developmentally relevant genes, 20 novel, end-sequenced cDNAs selected from a Day 10.5 postcoitum mouse embryo library were genetically mapped in intersubspecific backcross mice. Eleven of 20 cDNA clones mapped to three mouse autosomes (Chr 5, 11, and 14), a result that was unlikely (P < 0.03) if the distribution of genes expressed in embryos is random within the mouse genome. Several clones were candidates for mouse developmental mutations by virtue of genetic colocalization and concordance of embryonic expression patterns with the distribution of defects in mutant mice: Estm11 was a candidate for the mouse mutation wabbler-lethal (wl), since Estm11 mapped in the vicinity of wl on mouse Chr 14 and was expressed in those regions of embryonic brain that exhibit axonal degeneration in wl. End-sequence analysis, genetic mapping, and in situ hybridization appeared to be an effective combination of methods for identification and characterization of genes with potential regulatory functions during mammalian embryogenesis.