Environmental scanning electron microscopy (ESEM) has been applied to image the organization of spread films at the air-water interface directly. This recent extension of conventional scanning electron microscopy permits the resolution of electron microscopy to be applied to insulated and hydrated samples maintained in their natural state. ESEM therefore has great potential for the study of structure and dynamics of liquid surfaces. We have applied this novel technique to the in situ imaging of a nylon-6,6 polymer spread film as a function of surface concentration. To our knowledge, this is the first in situ ESEM study of a spread film on a liquid surface. The technique offers significantly better resolution over other in situ imaging techniques such as Brewster angle and optical microscopy and enables dynamic studies upon spread films in their natural state to be carried out. It was found that at all surface concentrations studied the individual nylon chains aggregate through hydrogen bonding to form microfibrils that align parallel to the water surface. At low surface concentrations (0.3-0.8 mg m(-2), corresponding to surface pressures pi similar to 0-2 mN m(-1)), these were dispersed in patches on the surface that moved randomly across the surface. As the surface coverage increased, the mobility of these islands reduced while they increased in size until the limiting surface coverage of 1.0 mg m(-2), at a nominal pi similar to 3 mN m(-1). At this concentration, a continuous film was observed where the microfibrils were close-packed. Higher 10 nm resolution images revealed that the distance between the microfibrils decreased with further concentration increases. The results obtained are qualitatively comparable to optical micrographs obtained by collapsing nylon-6,6 films under high surface pressure to form thicker films and to scanning force micrographs obtained from films deposited upon mica substrates. The findings are also supported by external reflection Fourier transform infrared studies. The experimental procedure and conditions for this novel experiment are given, and the results obtained are discussed in relation to those obtained from conventional methods.