The atomic force microscope (AFM) is increasingly used to image biological objects such as DNA, actin, membranes, and cells, in air or in liquid. It is very important that certain biological objects are observed in buffer, their "natural" environment. Xenopus oocytes form a good model system for expressing foreign genes, since their size easily allows the introduction of cDNA, coding for membrane proteins. Since oocytes are large objects, they have to be mounted so as to be immobilized during scanning by the AFM tip. We have used different supports for mounting Xenopus oocytes : pipettes, embedding in plexiglas, and gelatine. We have attempted to image the cell membrane of the oocyte with the AFM, but could only visualize the vitelline envelope and the yolk platelets. In the scanning electron microscope, we found that the cell membrane of the oocyte is rich in microvilli. The difficulty in imaging oocyte membrane with an AFM comes from the fact that the microvilli make the cell membrane of the oocyte very rough and deformable, thus creating instabilities for the tip during the imaging process. It thus seems impossible to image proteins that are inserted in the cell membrane of oocytes bearing microvilli. The use of oocytes with practically no microvilli may perhaps solve the problem of instability.