Impulse activity in axons generates aftereffects on membrane excitability that can alter the conduction velocity of subsequently conducted impulses. We used a computerized stimulus pattern (a 1 Hz stimulus period followed by a period of repeated short bursts at 200 Hz) to assess in vivo activity-dependent changes in conduction latency of functionally identified rat cutaneous afferents conducting in the A beta range. Several different parameters of activity dependence were measured: burst supernormality, the average increase in conduction latency following conditioning with a single preceding impulse during high frequency burst stimulation; burst subnormality, the average latency increase during each burst; depression, a long-term increase in latency caused by the high frequency stimulation. The data show that different mechanosensitive A beta afferents with overlapping resting conduction velocities exhibit activity-dependent changes in conduction latency that are characteristic of their particular functions.