The atomic force microscope is broadly used to study the morphology of cells(1-5), but it can also probe the mechanics Of cells. It is now known that cancerous cells may have different mechanical properties to those of normal cells(6-8), but the reasons for these differences are poorly understood(9). Here, we report quantitatively the differences between normal and cancerous human cervical epithelial cells by considering the brush layer on the cell surface. These brush layers, which consist mainly of microvilli, microridges and cilia, are important for interactions with the environment. Deformation force curves obtained from cells in vitro were processed according to the 'brush on soft cell model'(10). We found that normal cells have brushes of one length, whereas cancerous cells have mostly two brush lengths of significantly different densities. The observed differences suggest that brush layers should be taken into account when characterizing the cell surface by mechanical means.