A wide variety of commercial polymeric membranes are manufactured by a non-solvent immersion precipitation process, yet the detailed mechanism and kinetics of membrane formation are poorly understood. We have used a confocal microscope, with fluorescence filters removed, to observe backscatter from precipitating nylon 6 films. Nylon 6 in formic acid/water solutions was spread on a glass substrate, which was then quickly immersed into water or water/formic acid non-solvent baths. Two slope-casting chambers were designed in order to observe the precipitation process from both the substrate side and the bath side (in separate experiments). From the substrate side, a scattering front was observed to form within a few seconds after immersion, and then to progress toward the substrate as the precipitated film formed. When observed from the bath side, the scattering front first moved toward the bath for approximately 5-10s, then reversed direction and moved toward the substrate. This later motion toward the substrate can be explained by the contraction of the film as water is expelled. The initial motion toward the bath implies that the initial point of precipitation is not at the film surface, but rather at some depth (ca. 60 + mum) within the film. This new application of confocal microscopy has enabled measurements of the dynamics of nylon membrane precipitation with sufficient time and depth resolution to permit quantitative testing of models of the precipitation process.