Different diets low in lysine were fed to ducklings of various ages in three separate trials to investigate the effect of these diets on bodymass and subsequent reproductive performance. The results showed that when ducklings were fed a diet containing less than 0,40% lysine from day-old their bodymass was reduced significantly (P ≤5 0,01). When these same diets were fed to ducklings from 2 weeks and older no significant differences were noticed in bodymass. Feed intake was also reduced in proportion to the degree of lysine restriction and to age when first fed. Sexual maturity was delayed by lysine restriction but this did not cause an increase in average egg mass. The ducks on the low lysine diets laid fewer extra large and more smaller eggs than those ducks not restricted by lysine levels lower than 0,40%. The greatest disadvantage of feeding the low lysine diet was the high mortality rate. If this can be overcome the feeding system would be very economical.