Using atomic force microscopy (AFM) it has been possible to detect actin filaments that are beneath the cell membrane of living cells despite the fact that the AFM tip is applied to the surface of the cell. To determine whether the AFM tip actually penetrates or deforms the cell membrane we determined whether an intracellularly trapped fluorescent indicator was lost from cells during AFM. Using epifluorescence illumination to monitor the presence of fluo-3 in the cell, we found that AFM did not cause dye leakage from the cell. Further, force-distance curves indicated that standard tips did not penetrate the membrane while sharper Supertips TM did. In addition, the physiology of cells was found to be unaffected by AFM with standard tips since volume regulatory signal transduction mechanisms were intact in such studies. Thus, traditional AFM tips deform the cell membrane in order to reveal the presence of subcellular structures.