The US research raises the controversial prospect of a blood test providing early warning of suicide attempts.
Scientists said their results were "proof of principle" for a suicide test.
One particular molecule, an enzyme called SAT1, was linked to suicidal tendencies in a group of patients with bipolar disorder, a mental illness characterised by episodes of extreme high and low moods.
Study leader Dr Alexander Niculescu, from Indiana University, said: "In the future we want to study and assemble clinical and socio-demographic risk factors, along with the blood tests, to increase our ability to predict risk."
Meanwhile, British scientists said the research should be treated with caution.
Professor Keith Hawton, director of the Centre for Suicide Research at Oxford University, said: "I would say that the findings are of interest and may point the way to some future research based on large samples, but no more than that."