Psychophysical thresholds were measured as the frequency, size and duration of vibration on the thenar eminence was varied. The results supported the theory that there are two functionally distinct receptor systems in the skin for the perception of mechanical disturbances. Spatial and temporal summation were found for the detection of high- but not low-frequency stimuli. Furthermore, magnitude estimation data revealed that temporal summation occurs for the perception of high-frequency stimuli presented over a wide range of suprathershold values. On the other hand, temporal summation was absent for low frequency stimuli that were presented at 5, 10, 15, and 20 db above threshold.