Objective. Familial Mediterranean fever (FMF) is the most common auto-inflammatory syndrome with exaggerated acute phase and inflammatory response. After revealing the MEFV gene mutation with the finally disturbed end product pyrin, some of the mechanisms were explained. However it is still unknown what triggers or ends these periodical attacks. Moreover, the treatment of up to 30% of the patients, that are resistant to colchicine is still a problem. In this study we investigated the role of serotonin in colchicine-resistant FMF patients.