Otic bullas of the rat, obtained by excision and formalin fixed, are successfully embedded in methylmethacrylate by dehydration and subsequent infiltration with plastic under vacuum. Sections 10 microns thick are obtained by cutting the trimmed and sandpapered acrylic blocks on an LKB multirange microtome. The sections are collected on adhesive tape and stained with a Trichrome stain (modified Weigert-van Gieson). Finally, the sections attached to the tape are mounted on microscope slides with glycerin-gelatin and sealed in the same medium. Serial sections are used for three-dimensional graphic reconstruction.