This article reviews the studies on biochemistry & suicidal behavior. The authors describe findings about low serotonin, serotonin metabolite 5-HIAA, & dopamine metabolite HVA in completed & attempted suicide. They also outline evidence in depressed patients – in contrast to depressed, suicidal patients – there is no abnormality in levels of CSF 5-HIAA & corticosteroids. Studies on other monoamine metabolites are also discussed. (VM)