A series of experiments were carried out with the aim of evaluating chaya (Cnidoscolus aconitifolius) leaf meal (CLM), a fibrous protein-rich foodstuff, in terms of both digestibility and poultry performance as a potential ingredient to be utilised in poultry diets. In the first experiment, chaya plants at either 4, 8 or 12 weeks of re-growth were harvested. With the exceptions of ether extract and oxalic acid, no differences in chemical composition of the leaves were found between the different ages of re-growth for the contents of dry matter, crude protein, neutral detergent fibre, acid detergent fibre, lignin, ash or hydrogen cyanide. In experiment two, true metabolisable energy (TME) content as well as TME corrected to nitrogen equilibrium (TME_N) and dry matter and nitrogen digestibilities in CLM were evaluated in commercial broilers and criollo chickens. Neither CLM inputs nor genotype of the bird significantly affected the TME_N values. However, the collection period of droppings and the body weight of the bird significantly (P<0.05) affected TME_N. In experiment three, the effect of different fibre sources on endogenous losses of nitrogen, uric acid and amino acids as well as on energy balance and body weight loss were evaluated in cockerels. The different fibre sources caused significant (P<0.05) differences in all the dependent variables. An important fact, demonstrated by experiments 2 and 3, was that the endogenous losses of birds showed a very high variation; however, possible explanations for those findings were put forward. In experiment four, TME, net energy and heat increment values of CLM and wheatfeed were determined using cockerels in calorimeter chambers. Lower (P<0.05) values of TME and net energy were found in CLM compared to wheatfeed, and that was attributable to the different chemical composition of the ingredients evaluated and to the different properties of their fibre. In experiment five, the effect of different amounts of dietary CLM on apparent metabolisable energy (AME) of diets and on dry matter, nitrogen and amino acid digestibilities in broilers was evaluated.