The first observation of unstained cell membraneous structures by a scanning tunneling microscope is reported. An adhesive preparation method was used for imaging human medulloblastoma cells from the cell line TE 671 and oocytes from the clawed toad Xenopus laevis. The images show filaments, stacks of molecules and hilly structures. The possible identity of the filamentous structures is discussed, although the observed structures cannot yet be fully characterized. The work suggests possible future experiments on various biological structures in their natural environment. © 1989.