Suicidal behaviour has had, over time, different explanatory meanings. In ancient and feudal times, it took philosophical and religious meanings. Upon entry into modern times appeared explanatory sociological, medical and psychological meanings. Among the attempts to explain suicidal behaviour, especially in the last half century, there are also the biological landmarks. Objective: Synthesizing the biological research results in a small explanatory set. Material and methods: Data is collected from literature. Results and conclusions: On the basis of suicidal behaviour, there are nonspecific genetic vulnerabilities, found also in specific mental illnesses that favour, at a different level, the developing of nonspecific neurotransmitter vulnerabilities which, in turn, favour not the suicidal decision, but the progress of this behaviour.