We have previously reported the unusual combination of low urinary free cortisol levels with high urinary norepinephrine excretion in posttraumatic stress disorder (PTSD) patients in comparison with four other patient groups: major depressive disorder, endogenous type; bipolar I, manic; paranoid schizophrenia; undifferentiated schizophrenia. Cortisol levels alone did not distinguish PTSD from paranoid schizophrenia patients and norepinephrine levels alone did not distinguish PTSD from bipolar I, manic, patients. In further consideration of these findings, we have found that combining the values for the two systems in a norepinephrine/cortisol (N/C) ratio provides a measure that significantly distinguishes PTSD from all the other patient groups throughout the hospitalization period. The N/C ratio was more than twice as high in the PTSD group than in all the other patient groups in the first sample following hospital admission, in the mean sample during hospitalization, and in the last sample before discharge. The mean N/C ratio for the PTSD group was 2.54, compared with a mean of .99 for the other four groups, which ranged from .81 to 1.18. The diagnostic sensitivity was 78% and the specificity was 94% for correct classification of PTSD in our sample. These preliminary findings yield further encouragement for exploring multivariate strategies, using hormonal ratios or profiles, in an effort to increase the diagnostic sensitivity of neuroendocrine criteria in the assessment of psychiatric patients.