This project is designed to determine how first and second pain, evoked by a brief heat pulse, are influenced by parameters of peripheral stimulation. Brief painful stimuli are presented to the hands and feet of human subjects. These consist of constant waveform heat pulses that raise skin temperatures of one cm2 area of skin to noxious levels (45-49 degrees C) for 0.7 sec. No tissue damage is produced. Reaction times and pain magnitude estimations (dependant variables) are made in response to these heat pulses. Independant variables include interpulse interval and location of stimulation site. Data are analyzed with the aid of an on-line computer system.