The effects of body size and feed intake on N digestibility, pancreas and liver weight, and digestive enzyme activities in male broiler chicks were compared with those induced by dietary tannins. Four groups (SSM, ad lib., pair-fed and young) of sixteen birds each (2 weeks old) were used as experimental animals. They were fed on experimental diets for 4 weeks, except the young group which were fed from age 15 d to 24 d only. Two isonitrogenous and isoenergetic diets with (SSM) or without salseed (Shorea robusta) meal (CONTROL) were used. SSM diet was fed ad lib. to SSM group and control diet was fed ad lib. to ad lib. and young birds and to pair-fed birds at same intake level as SSM birds. Birds fed ad lib. utilized their diet more efficiently than the SSM and pair-fed birds. Digestibility of N, both apparent and ileal, was substantially lower with SSM diet than with the control diet. Each of the treatments induced enlargement of the pancreas (g pancreas/kg live weight) when compared with ad lib. birds. There was no difference between the relative liver weights of SSM and ad lib. birds; however, pair-fed and young birds had comparatively bigger livers. In pair-fed birds the trypsinogen activity of pancreatic tissue (U/g pancreatic tissue) was significantly depressed but there was a significant elevation in trypsinogen (U/kg live weight) activity in SSM birds; again pair-fed birds exhibited the lowest value for this variable. Compared with control birds all the other treatments resulted in significant depression of α-amylase (EC 3.2.1.1) activity in pancreatic tissue (U/g) and jejunal digesta (U/g), but because of pancreatic enlargement α-amylase activity per kg live weight was significantly lower only in SSM birds. The activity of trypsin (EC 3.4.21.4) in jejunal digesta was very low in SSM birds, but it was slightly higher in the young birds. Dipeptidase (EC 3.4.13.11) and disaccharidases in duodenal and jejunal mucosa were markedly depressed by the diet containing salseed meal, with the exception of maltase (EC 3.2.1.20) which was unaffected in jejunal mucosa. Enterokinase (EC 3.4.21.9) activity was not inhibited by the presence of tannins in the diet, rather it increased in the duodenal mucosa of SSM birds.