Methods are described for measuring the initial velocity, angular velocity, projection angle and air resistance coefficient of explosively dispersed seeds of Hura crepitans. The methods are generally applicable to any explosively dispersed seeds. In Hura the initial velocities were normally distributed about a mean of 43 ms−1 and in one case exceeded 70 m s−1. Although projection angles are not constant, the mean of 34° above horizontal lies close to the optimum for maximum dispersal, and the frequency of angles less than 0° or more than 50° are negligible. Angular velocities are high, attaining at least 15,000 rpm in one case. The resistance coefficient could not be measured precisely, but was probably between 0.087 and 0.118 m−1. The maximum dispersal distance recorded was 45 m from the parent tree, with a marked modal dispersal distance at about 30 m. The ecological implications of explosive dispersal are briefly discussed.