Pigs of 50 lbs. initial wt., fed on coarse, medium and finely ground oats, adequately supplemented by proteins and minerals, showed significantly faster gains as the modulus became finer. Pigs fed coarse, medium, and fine modulus attained live wts. of 121, 132, and 155 lbs., respectively, in 60 days of feeding. Greater feed consumption by pigs on fine modulus was attributed to the increased size of the pigs because of faster growth rates. Unless finely ground, the fibrous portions (largely hulls) were decidedly unpalatable to younger pigs, and were sorted out and refused. Grinding to various moduli did not affect the dry matter digested by older pigs, and when, because of fine grinding, the young pigs could not separate the hulls, no age differences were noted in dry matter digestibility. The importance of considering feed refusals is demonstrated. When refused feed was considered as feces, there was an increase of about 3% in the digestibility between each modulus of grinding, with the coarse grind being the least digestible. Most of this increase in digestibility with finer grinding could be accounted for by the greater digestibility of the carbohydrate fractions. The possibility of a factor, or factors, contained in oat hulls, affecting nutrient utilization is discussed.