Three experiments were carried out on sheep in which the rate of degradation of dry matter and fibre fractions of dehydrated whole maize plants (DWM) using a nylon bag technique (experiment I), digestibility of the dietary nutrients in the gastro-intestinal tract (experiments II and III) and its particular parts (experiment II) were studied. The animals were fed diets containing DWM and rapeseed oilmeal (R), fish meal (F), a barley-urea preparation (U) or a control diet containing only DWM (C). Diets R, F and U were isonitrogenous and isocaloric. The dietary nitrogen source did not affect ruminal degradability of the maize fibre fractions in sacco (experiment I), however greater digestibility of crude fibre, NDF, ADF and cellulose in diets R and F than in U or C was found (experiment II). Intestinal digestibility of fibrefractions and its ratio to whole tract digestibility were higher in the urea-containing diet than in the remaining diets. Although whole tract digestibility of fibre fractions did not depend on the dietary protein source (experiments II and III), digestibility of fibre fractions was found to be significantly lower in sheep fed diet C as compared with those given diets R, F or U.