GENETIC deafness is common, affecting about 1 in 2,000 births¹. Many of these show primary abnormalities of the sensory neuro-epithelia of the inner ear, as do several hearing-impaired mouse mutants, suggesting that genes involved in sensory transduction could be affected. Here we report the identification of one such gene, the mouseshaker-1(shl) gene. Shaker-1 homozygotes show hyperactivity, head-tossing and circling due to vestibular dysfunction, together with typical neuroepithelial-type cochlear defects involving dysfunction and progressive degeneration of the organ of Corti^2–7. The shl gene encodes an unconventional myosin molecule of the type VII family. Three mutations are described, two mis-sense mutations and a splice acceptor site mutation, all in the region encoding the myosin head. The myosin type VII molecule encoded by^shl is the first molecule to be identified that is known, by virtue of its mutations, to be involved in auditory transduction.