Maresin conjugates in tissue regeneration 3 (MCTR3) is a specialized pro-resolving mediator (SPM) synthesized from docosahexaenoic acid in macrophages. DHA is oxidized to maresin 1 , which is converted to MCTR1 by glutathione S-transferase Mu 4 or leukotriene C4 synthase, then to MCTR2 by γ-glutamyl transferase, and to MCTR3 by dipeptidase. MCTR3 accelerates tissue regeneration in planaria (1 and 100 nM) approximately as potently as MCTR2 and more potently than MCTR1. Pretreatment with MCTR3 prior to E. coli administration in mice reduces neutrophil infiltration, shortens the inflammatory resolution period, and increases phagocytosis of E. coli by macrophages. When administered at a dose of 100 ng 12h post E. coli infection in a mouse model of peritonitis, MCTR3 selectively reduces the amount of the eicosanoids PGD2 , PGE2 , PGF2α , and TXB2 in the exudate.