The capabilities of the scanning tunneling microscope as a tool to study the morphology and structure of adsorbed biomolecules are reviewed in view of recent experimental results. Problems such as electrical conductivity of the biomolecules, fixation to the substrate and identification are analyzed in detail. In particular, the role of tip-surface interaction giving rise to repulsive forces is illustrated. It is concluded that fixation rather than conductivity is the major obstacle to the use of the STM for biological imaging. © 1990, American Vacuum Society. All rights reserved.