Loudness dependence of auditory evoked potentials (LDAEP) is a validated in vivo marker of central serotonergic function. We aimed at measuring serotonergic activity in a follow-up study of suicidal patients. It should be investigated whether suicide attempts or suicidal states cause changes in the LDAEP. Thirteen patients (mean age, 40.9 ± 11.3 years; age range, 20-61, 6 male) with a major depressive episode who had attempted suicide or had suicidal plans (Hamilton Depression Rating Scale item 3 [suicidality] ≥3) were included in the study. LDAEP and psychometric measurements took place about 2, 5, 9 and 16 days after attempted suicide or suicidal action. On day 9, LDAEP was significantly higher compared to day 2 and day 16; there was a similar tendency compared to day 5. Instability of central serotonergic function is suggested resulting in reduced serotonergic activity about 1 week after suicide attempt. Further studies are necessary that include larger samples in order to distinguish between different psychiatric diseases and to consider confounding factors like gender, smoking, medication, impulsivity or lethality of suicidal action.