This study investigated the effects of daily administration of three grams of tryptophan in conjunction with a high carbohydrate, low fat, low protein diet on chronic maxillofacial pain, experimental pain thresholds, and anxiety and depression. In a double-blind study, 30 chronic pain patients were randomly assigned to a tryptophan or placebo group. At the initial appointment and 4 weeks later, the patients' subjective ratings of their pain were recorded, electrical tooth pulp stimulation was used to measure pain thresholds, and psychological tests of depression and anxiety were administered. Over the 4 weeks of the study, there was a greater reduction in reported clinical pain and a greater increase in pain tolerance threshold in the tryptophan group than in the placebo group. The group did not differ in anxiety and depression--for all subjects there was lowered depression and anxiety over the 4 weeks of study.