We evaluated objective criteria for defining points for needle insertion prior to conducting a multisite clinical trial of auricular acupuncture for cocaine addiction. Thirty-four cocaine-abusing subjects participated in a study in which the trial's active zones (Shenmen, Liver, Lung, and Sympathetic) and control zones (located on the ear helix) were divided into quadrants and assessed along four dimensions: electrical resistance, skin discoloration, skin topography, and tenderness. Acute effects of needles inserted into points of low electrical resistance in one ear and high electrical resistance in the other were also assessed. Results showed that the active zones had lower overall electrical resistance and more subcutaneous ridges than control zones. Zones did not possess significant variability along any single dimension. Acute effects of needling high and low resistance points were similar, differing only for "fullness." Based on these findings, and in view of the difficulty of accurately measuring electrical resistance at ear points, we do not recommend the use of electrical devices for point determination in the multisite study. At present, there seems to be little scientific basis for the preselection of specific points for needle insertion within auricular zones. Needle placement should be based upon clinical judgement.