Diurnal variation in the chemical composition of digesta and its e †ect on nutrient digestibilities of diets varying in dietary Ðbre content was examined in pigs Ðtted with a PVTC-cannula at the terminal ileum. The pigs were fed three times a day (08 : 00, 16 : 00 and 24 : 00 h). A barley control diet and four barleybased diets containing two levels (100 or 200 g kg~1 diet) of alfalfa meal or white clover meal and as an indigestible marker were fed according to a 5 ] 5 Cr 2 O 3 Latin square design. In each experimental period, digesta were collected for 1 h every third hour on each of two separate sampling days, covering in total a 24 h period. The concentration of dry matter (DM), crude protein (CP), ash and chromium (Cr) in the ileal digesta varied in relation to time of feeding. However, the patterns were similar after all three meals (08 : 00, 16 : 00 and 24 : 00 h) and independent of diet. The maximum DM, CP and ash contents were reached 4È5 h post-feeding. The highest (P \ 0É05) DM concentration was found in the ileal digesta of pigs fed the barley control diet. The DM concentration decreased (P \ 0É05) as the inclusion level of alfalfa meal and white clover meal was increased. The lowest DM concentration was found for the highest inclusion level of alfalfa meal. The ileal digestibilities of both organic matter and CP were lower 1È2 h post-feeding compared with those recorded 3È5 h later, indicating that the less digestible components of a diet have shorter transit times. The pooled ileal digestibilities of organic matter and CP from the three 8 h periods (08 : 00È16 : 00 h, 16 : 00È24 : 00 h, 24 : 00È08 : 00 h) did not di †er (P \ 0É05) from each other. Therefore, the estimate of digestibility can be based on digesta samples collected from any interval between two consecutive meals. However, care must be taken to obtain representative samples of digesta between meals.