Measurement of the catecholamine's, norepinephrine, epinephrine, metanephrine, normetanephrine, vanilmandelic acid, and 3-methoxy-4-hydroxyphenyl-glycol (MHPG) show certain statistical correlations with three clinical diagnoses. These conditions are as follows: 1) bipolar and schizo-affective depression, 2) unipolar nonendogenous depressions, and 3) schizophrenia related depressions. More specifically MHPG acts to predict which patients will require higher doses of medication, higher plasma levels, and longer treatment periods to respond to treatment.