The influence of stimulus velocity and traverse length on the ability of human subjects to indicate in which of two opposite directions a brush moved along the skin was determined using a forced choice procedure. Stimulus velocities ranged from 0.75 to 250 cm/sec, and traverse lengths ranged from 0.5 to 6 cm; measurements were made on both the thenar eminence and the preaxial upper arm. Performance was expressed in terms of "critical traverse length" i.e., that traverse length at which, for a given velocity, the subject would correctly identify the direction of brush motion on 75% of the trials. The data indicate that the capacity to identify direction of tactile stimulus motion increases with traverse length and is optimal for velocities between 3 and 25 cm/sec. The overall level of performance was better on the thenar than on the upper arm.