2. What are the relative effects of opioids and mexiletine on affective and cognitive function in patients with amputated extremities? Using established tests of neuropsychological function, mood, and psychosocial and physical impairment, affective and cognitive changes associated with the opioid and mexiletine therapies will be quantified and compared with changes associated with placebo treatment. These studies will help determine if the effects of opioids and mexiletine on affect and cognition are likely to limit the usefulness of the medications in the treatment of pain following amputations.