Three milk substitutes (control, pea and soya-bean) were given to 6 preruminant calves fitted with re-entrant canulas in the terminal ileum. In the control diet, protein was almost entirely provided by skim milk powder. In the pea diet, a pregelatinized dehulled pea flour provided 33.5% of the protein, the remainder being supplied by skim milk powder. In the soya-bean powder diet 73.2% of the protein were provided by a soya-bean isolate and the remainder by whey powder. The apparent digestibility of total nitrogen was significantly lower with the pea and soya-bean diets. than with the control diet (0.92, 0.91 and 0.95 at the end of the ileum, 0.92, 0.94 and 0.97 at the end of the whole digestive tract, respectively). Also the ileal digestibility of most amino acids decreased with the pea and soya-bean diets; the differences were greatest for cystine (-0.6; non significant) with the pea diet and for threonine (-0.7; P less than 0.01) with the soya-bean diet. Irrespective of the diet the protein escaping digestion in the small intestine appeared to be mainly from endogenous and bacterial origin. Although small amounts of partially degraded dietary protein could be present in ileal digesta with the pea and soya-bean diets, their true digestibility was probably very high.