Concentrations of 5-HIAA, HVA, & HMPE in lumbar spinal fluid were measured by mass fragmentography in 16 men convicted of criminal homicide, 22 men who had attempted suicide, & 39 healthy controls. Those who had killed a sexual partner or who had attempted suicide had lower levels of 5-HIAA in spinal fluid than controls. It is suggested that low levels of 5-HIAA reflect a disorder of serotonin turnover which makes the individual more prone to acts of violence in states of emotional turmoil.