Richner-Hanhart's syndrome. Electron microscopic study of the skin lesion. The plantar hyperkeratotic skin lesion in a case of Richner-Hanhart's syndrome was investigated using ultrastructural examination. Light microscopic examination showed remarkable hyperkeratosis and some aberrant keratinocytes with multiple nuclei. On ultrastructural examination, some abnormal structures were seen in the affected keratinocytes: aggregations of tonofilaments and intracytoplasmic inclusions. The inclusions were needle shaped and were considered to be "crystal ghosts," presumably of tyrosine. The formation of tyrosine crystalline inclusions seems to be an important factor in the pathogenesis of the cutaneous lesions in Richner-Hanhart's syndrome. 