This study examined the correlation of progesterone (a hormone) with suicidal ideation & behaviours in a sample of 160 high school students. Subjects answered a questionnaire & provided a blood sample. Progesterone levels were clearly higher in male subjects who had attempted suicide or who were thinking about suicide. In contrast, in female subjects, progesterone was correlated with not having attempted suicide & not talking about wanting to kill oneself. Possible explanations are discussed.