To evaluate the relationship between plasma serotonin levels & psychometric measures in suicidal adolescents versus controls, 211 Israeli adolescents were divided into 4 groups: 35 suicidal psychiatric inpatients; 30 nonsuicidal psychiatric inpatients; 51 adolescents referred to the emergency room after an attempt; & 95 community-based controls. Plasma serotonin levels were significantly lower in the control group compared to all other groups. A significant negative correlation was found between plasma serotonin level & suicidal behaviour severity among the suicide inpatients. Gender, depression, & anger were associated with suicidal behaviour in all 4 groups. Beck Depression Inventory scores together with plasma serotonin levels discriminated between healthy controls & other groups. (49 refs.)