Particle diffusion of six sizes of nylon particles was observed, recorded, and analyzed. The experimental apparatus was designed and the particles were selected to achieve the following: (a) restriction of the particle motion to a horizontal plane thereby eliminating the effect of gravity; (b) elimination of particle-to-particle collisions by observing the motion of widely separated individual particles; (c) elimination of the effect of particle density by using nearly neutrally buoyant particles; and (d) a homogeneous and isotropic field of fluid motion in which particle diffusion occurs without mean motion. The motion of individual particles was recorded on motion-picture film, which was subsequently projected for displacement measurements. (Author Modified Abstract)