Anserinase (Xaa-methyl-His dipeptidase, EC ) is a dipeptidase that mainly catalyzes the hydrolysis ofNa-acetylhistidine in the brain, retina and vitreous body of all poikilothermic vertebrates. The gene encoding anserinase has not been previously identified. We report the molecular identification of anserinase, purified from brain of Nile tilapia Oreochromis niloticus.