D-phenylalanine (DPA) is known to block the activity of carboxypeptidase, an enzyme which degrades enkephalins, endogenous morphine-like substances. Therefore, it is considered that DPA administered as an inhibiting drug of this degrading enzyme might prolong analgesia induced by acupuncture. 1) Thirty patients suffering from chronic low back pain were treated with acupuncture 30 minutes after the oral administration of 4.0 grams of DPA. The results were: excellent in 7 cases, good in 11, fair in 6 and poor in 6. Cases graded excellent and good were then compared with a placebo group. The effect was increased 26% in the DPA-acupuncture group, which shows no statistically significant difference (P less than 0.1). 2) In 56 patients, tooth extraction was performed under acupuncture anesthesia: 18 had received 4.0 gram of DPA (P.O.) 30 minutes earlier. The results were excellent in 8, good in 6, fair in 3, and poor in 1. The excellent and good cases were compared with 38 placebo group cases. The effect in the DPA-acupuncture anesthesia group was significantly increased by 35% (P less than 0.01). 3) In order to determine the optimum time for the administration of DPA, two schedules of administration were compared. [1] DPA was given on the previous day in three 0.5 gram doses (26 cases). [2] A single 4 gram dose was administered 30 minutes before treatment (30 cases). The results from the "excellent", "good" and "fair" cases showed a 16% increase in effectiveness when DPA was administered the day before, not a statistically significant difference (P less than 0.1), but a clear tendency to increase was observed. The above findings show that DPA has an enhancing effect on acupuncture analgesia and anesthesia in clinical practice.