Abstract Background: Prolactin and cortisol responses to d-fenfluramine challenge of central serotonin are reduced in depressed and suicidal patients. Low serum cholesterol levels are also reported in suicidal behavior. Thus, we examined for a relationship between serum cholesterol and fenfluramine challenge responses in patients with depression and/or attempted suicide. Methods: We studied 12 patients and six controls. Blood was drawn for baseline serum cholesterol and the d-fenfluramine challenge test performed. Results: Serum cholesterol levels were significantly lower in suicidal patients than in either non-suicidal patients or controls. However, neither the prolactin nor cortisol responses to d-fenfluramine correlated significantly with serum cholesterol levels. Conclusion: No relationship was found between serum cholesterol and these peripheral indices of serotonergic function.