Reports on the efficacy of the Minnesota Multiphasic Personality Inventory (MMPI) for selecting patients with valid complaints of pain, have been equivocal. The Mensana Clinic Screening Test for Chronic Back Pain Patients (MPT) was able to predict, with some degree of success, patients who had definite organic pathology. However, ther MMPI measures personality traits, while the MPT measures the impact of pain on a patient's life. In order to determine which of the two tests would be a better predictor of actual physical abnormalities, and hence valid pain complaints, a comparison was undertaken between the two tests. The charts of 53 female admissions to the Neurosurgery Service of Johns Hopkins Hospital, with the complaint of back pain, were assessed. MMPI test results, as well as test results for the MPT, were compared to the presence or absence of pathology on electromyography, nerve conduction velocity studies, thermography, myelogram, CT scan, or X-ray. The MPT had a correlation factor of -0.5384, that was significant at the 0.00002 level. Of the 30 patients scoring 17 points or less on the MPT, 77% had objective physical abnormalities, considered moderate or severe by blind review. Of the 23 patients scoring 18 points or greater on the MPT, only 18% had objective physical findings that were considered moderate or severe. Only the depression scale (scale no. 2) of the MMPI correlated with objective physical abnormalities (R = -0.30). However, only 58% of the patients with T scores on scale no. 2 of less than 70 had objective findings, while 56% of patients with T scores greater than 70 had objective physical findings.(ABSTRACT TRUNCATED AT 250 WORDS)