The growth of broiler chickens on diets containing various levels of Lemna gibba was evaluated. Groups of broiler chicks were fed on diets containing 0-400 g Lemna gibba/kg for 3 weeks. These chickens were then changed to standard diets for a further 2 weeks. As the level of Lemna gibba increased, feed consumption and weight gain decreased. However, when diets were changed to the standard diet, compensatory growth was observed. In a second experiment, diets were formulated with a metabolizable energy of 5.02 MJ (1200 kcal)/kg Lemna gibba and included a finer-milled Lemna gibba. Chickens were fed on diets containing 0-300 g Lemna gibba/kg for 4 weeks. Each group was then divided into two subgroups. For the next 2 weeks one of these sub-groups was maintained on the experimental (Lemna gibba) diets (LL), while the other sub-group was changed to a standard diet (LS). Bird fed at levels above 150 g Lemna gibba/kg had decreased consumption and weight gain. These birds when changed to a standard diet tended to have increased weight gain compared with chickens continuously fed standard rations. LS birds had significantly higher weight gains and feed consumption and lower feed conversion than LL birds. In contrast to older birds, chicks fed on Lemna gibba at high concentrations showed growth retardation. When changed back to a standard diet they demonstrated normal or compensatory growth.