['Depression is accompanied by a depletion of n-3 poly-unsaturated fatty acids (PUFAs). There is also a negative correlation between suicide and fish-oil intake (rich in n-3 PUFAs) across different countries. Both depression and suicide show a seasonal variation and are related to disorders in the serotonergic system.', 'The present study was carried out to determine if there is a seasonal variation in the PUFA fractions in serum phospholipids and whether there are significant relationships between lowered n-3 PUFA status and the seasonal variation in the number of suicide deaths and serotonergic markers of suicide.', 'We took monthly blood samples during 1 calendar year from 23 healthy volunteers and analyzed the PUFA composition in serum phospholipids and related those data to the annual variation in the mean weekly number of suicides for Belgium and the Bmax [3H]-paroxetine binding to platelets in the same 23 subjects.', 'Significant annual rhythms were detected in the long-chain PUFAs only, i.e. arachidonic acid (C20: 4n-6; AA), eicosapentaenoic acid (C20: 5n-3; EPA), and docosahexaenoic acid (C22: 6n-3; DHA). There was a significant correlation between the changes over the last 2 weeks in AA and EPA and the mean weekly number of violent, but not nonviolent, suicide deaths in Belgium. There was a significant correlation between the PUFAs, AA and DHA, and the Bmax [3H]-paroxetine binding to platelets.'] Is in humans , the seasonal variation in poly-unsaturated fatty acids related to the seasonal variation in violent suicide and serotonergic markers of violent suicide?