We examined the practical scan speed for the observation of live neurons in a physiological solution using atomic force microscopy (AFM) with a desired vertical resolution of the order of 10(-8) mi which was reasonable when taking into account that a flicker of extracellular protein and saccharide on the neurons in the solution occurred during an observation period of a couple of minutes. The practical scan speed was found to be under 40 mu m/s, therefore, if we applied AFM using 100 lines and 100 pixels per line to an observation area of 20 mu m x 20 mu m, the minimum period for acquiring one image was estimated to be about 2 min. This procedure gave us good images that represented the slow three-dimensional dynamics in live neurons, such as the retrograde movement of surface protuberances, but suggested that another approach was required to detect fast structural changes induced by stimulation.