Eighteen subjects distressed by memories of a specific traumatic event were randomly assigned to a single session of one of three conditions: Eye Movement Desensitization and Reprocessing (EMDR), a Time Interval Condition (TIC), or Tapping Alternate Phalanges (TAP). All subjects treated in the EMDR group showed desensitization as monitored by SUDs, which correlated with the physiological data and cessation of pronounced symptomatology. Only one subject in a control group showed desensitization. Compared to TIC and TAP, autonomic measures showed distinct changes during EMDR: (1) respiration synchronized with the rhythm of the eye movements in a shallow, regular pattern; (2) heart rate slowed significantly overall; (3) systolic blood pressure increased during early sets, invariably declined during abreactions, and decreased overall; (4) finger tip skin temperature consistently increased; and (5) the galvanic skin response consistently decreased in a clear "relaxation response". This relaxing effect of the eye movements suggests that at least one of the mechanisms operating during EMDR is desensitization by reciprocal inhibition, by pairing emotional distress with an unlearned or "compelled" relaxation response.