Norepinephrine and epinephrine were measured serially in 24-hour urine
collections from 99 male psychiatric inpatients with mixed diagnoses. The
group was blindly divided into those with a previous history of at least
one suicide attempt (N = 38) and those without such a history (N = 61). The
ratio of norepinephrine-to-epinephrine levels was significantly lower in
the group with a history of suicide attempts. The authors discuss the
possibility that a low norepinephrine-to- epinephrine ratio is a risk
factor for suicidal behavior.