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 1·5 g/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 182·2 g, 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 1·5 g/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 2·4–3·9 g 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.