The accretion of methionine and protein as a function of methionine intake was assessed in growing ducks between 22 and 42 d post-hatching. Four graded doses of DL-methionine at 0, 0–5, 1–0 or 1–5g/kg diet were added to a methionine-limiting basal diet and fed to four replicate groups of four ducks each. The growth and efficiency of food use for growth increased linearly (P <0–05) as a function of methionine intake. The accretion of body protein increased (P <, 0–001) from 87–5 to 182–2g, and that of methionine from 1616 to 3125 mg, over the 21 d period as dietary methionine increased. The accretion rate of methionine in the body (y, mg/d) as a function of methionine intake (x, mg/d) of ducks fed diets containing supplemental methionine at 0, 0–5, 1–0 or 1–5g/kg diet from day 22 to day 42 post-hatching gave the regression equation: y = - 148–86 (SE 32–558) + 0–312 (SE 0–0384)X, r2 = 0–8253. For protein accretion rate in the body (y, mg/d) as a function of methionine intake (x, mg/d), the regression equation was: y = - 9782 (SE 2204) + 19–505 (SE 2–5994)x, r2 = 0–8009. There was a linear relationship between methionine (y, mg/d) and protein (x, mg/d) accretion in ducks that was described by the equation y = 12–757 (SE 7–4019) + 0–01 525 (SE 0–00 107)x, r2 = 0–9355. The results of these studies suggest a constant utilisation of methionine over the range 2–4-3-9g digestible methionine/kg diet, with an efficiency of 31%. Furthermore, the results suggest a quantitative relationship of 15 mg methionine for every gram of protein accretion.