Twelve newborn Holstein bull calves were used to evaluate the effects of dietary abrasiveness, determined by a new method, on ruminal development. Calves were blocked by age and body weight and were assigned to one of three different diets. Each diet had the same ingredients but different particle sizes, which resulted in different abrasive values. No differences were detected in molar percentages of volatile fatty acids in ruminal fluid or in plasma concentrations of urea, glucose, or beta-hydroxybutyrate. The pH of ruminal fluid was lower for calves fed the fine and intermediate diets than for those fed the coarse diet. Digesta-free weights of the stomach and stomach compartments were similar among calves fed the three diets, except that omasum weights were heavier for calves fed the fine diet. Length of the ruminal papillae increased as the abrasive value of the diet decreased. Measurements of ruminal tissue layers from the ventral floor of the cranial sac were not different among diets, but the keratin portion represented more of the epithelial layer for calves fed the diet with the lowest abrasive value, thus decreasing the percentage of metabolically active tissue for those calves.