This study evaluated the effect of supplementing increasing levels of L-methionine (L-Met) in the diet for Muscovy ducks from hatch to 21 days of age. A total of 90 male Muscovy ducklings were assigned to 30 pens with 3 birds per pen. A basal diet with corn, soybean and wheat by-product was supplemented with 0, 0.08, 0.16, 0.24, 0.32 and 0.40% L-Met, obtaining 6 diets with increasing concentrations of sulfur amino acids, but constant in energy and other essential nutrients. Analysis of variance and Tukey's mean comparison test were performed. In addition, an effective dose-response model was performed to determine the optimal methionine level. Body weight and feed intake were not influenced (p>0.05) by L-Met supplementation, although a numerical trend towards greater weights was observed as supplementation increased. Feed conversion was significantly better with 0.24 and 0.32% L-Met s...