abstract - this work was conducted to evaluate the effects of different concentrate levels on the liquid passage rates, using co-edta, and particulate, using ytterbium chloride and cr-mordant, and the in situ ruminal degradation kinetics of dry matter (dm) and crude protein (cp). five rumen and abomasum fistulated bull holstein calves, with an initial average age of 5.8±0.7 months and initial average of 107.4±11.0 kg lw were allotted to a 5x5 latin square design (treatment x period). the animals were housed in individual stalls and full fed diets (dm basis) containing 30.0, 45.0, 60.0, 75,0 and 90.0% of concentrate. the diets were based on coast-cross grass hay as forage and soybean meal an corn ground grain in the concentrate. the passage rate of fluids showed a quadratic behavior, with the maximum value of 9.73%/h, with the 61.69% of concentrate in the diet. the particulate passage rate of the soybean meal in the reticulum-rumen linearly decreased, while the concentrate levels in the diets did not affect the passage rate in proximal cecum-colon. the concentrate levels in the diet did not affect the passage rates of the coast-cross grass hay in the reticulum-rumen and in the proximal cecum-colon. the effective degradation of the dm of the soybean meal was not affected, while those of the corn ground grain increased and coast-cross grass hay linearly decreased, respectively. the effective degradation of the cp of the soybean meal and coast-cross grass hay did not vary, however, that of the corn ground grain linearly increased as the dietary concentrate levels increased.