Although atomic force microscopy (AFM) has been successfully applied t
o a number of biological specimens under aqueous solution, its resolvi
ng power has been limited due to specimen deformation or damage induce
d by the scanning tip, especially with large flexible and heterogeneou
s specimens. To further expand the capabilities of the AFM, a cryo-AFM
was recently developed to operate under ambient pressure in liquid ni
trogen vapor. The operating principle of this novel system is discusse
d, and some of the most recent applications of the cryo-AFM to various
biological specimens are reviewed. These results have clearly demonst
rated the power of the cryo-AFM in the study of biological structures,
and at the same time, have revealed novel structural information of s
everal important molecules.