Background: Abnormalities in the serotonergic (5-HT) system have been implicated in the pathogenesis of suicidal behavior. Studies on peripheral serotonergic parameters as a measure for central serotonergic function in suicidal patients appear to be promising, yet failed to show a clear association with suicidality. The objective of this study was to elucidate the role of serotonergic blood parameters in depressed suicidal patients and to examine their usefulness as a potential biological marker for suicidality. A number of personality traits were assessed in order to provide a basis for a psychobiological model of suicidal behavior. Methods: Depressed patients with a recent suicide attempt (SA; n = 59) were compared to those without history of suicide attempts (NSA; n = 28). 5-HT_2A receptor binding in platelets and tryptophan/amino acid ratio in plasma were measured. Acute psychopathology and personality traits as well as characteristics of suicide attempts were assessed. Results: There was no significant difference between SA and NSA in terms of peripheral serotonergic parameters as well as personality traits. However, the whole sample showed associations between certain personality traits and serotonergic platelet parameters. Furthermore, we observed a relation between suicidal ideation, lethality of suicide attempts and peripheral serotonergic markers. Limitations: The number of cases with data on peripheral markers is relatively low. The potential influence of antidepressant medication previous to study inclusion has to be taken into account. The study focussed on depressed patients only. Conclusions: Low serotonergic function is involved in the pathogenesis of suicidality, whereas the use of platelet 5-HT_2A receptor activity and tryptophan availability as biological markers for suicidality in depressed patients could not be proven an appropriate tool. Alterations in the serotonergic system are associated with trait aggression and other character dimensions.