Lowered serotonin turnover has been observed in impulsive hetero- and auto-aggressive behavior. Most notably the CSF 5-hydroxyindole acetic acid concentrations were decreased. However, data on CSF or blood serotonin are far from clear-cut, since similar levels in suicidal and non-suicidal patients have also been noted. Longitudinal studies of suicidal patients have revealed pronounced shifts in blood serotonin levels, whereas healthy subjects' blood serotonin levels remained stable. We investigated blood serotonin levels of female schizoaffective patients and healthy women to test whether the fluctuations correlated with changes in autoaggressive behavior. The patients were divided into three groups: nonsuicidal, acutely suicidal, and postsuicidal. Nonsuicidal and postsuicidal schizoaffective patients' and healthy women's blood serotonin levels were similar. Suicidal patients' blood serotonin levels were significantly lower than those of healthy subjects and postsuicidal patients. We interpret the serotonin augmentation after a suicide attempt as a psychobiological correlate of increased neurotransmitter function.