Macromelanosomes in a spindle and epithelioid cell nevus, which occurred in the electron beam‐damaged skin of a woman with mycosis fungoides, were ultrastructurally investigated. The melanosomes in the spindle and epithelioid cells were varied in size but uniformly spherical in shape and composed of a core and cortex structure. Electron‐lucent bodies were observed in the small melanosomes as well as in the macromelanosomes. Positive dopaoxidase reaction was revealed on the cortex of these melanosomes and partly on their electron‐lucent bodies. The electron‐lucent bodies were not vesicular structures but were aggregates of filamentous elements, which had a continuity with fibrous structures in the melanosome cortex. It is concluded that the electron‐lucent bodies may be one of the matrices of melanization. Anomalously large accumulations of these bodies and concentrical melanization seem to lead to the formation of macrome