Two feeding trials were conducted involving diets supplemented with soybean meal, dried brewers, and wet brewers grains. The first trial involved 24 first-calf heifers averaging 82 d postpartum. After a 20 d protein depletion period in which a 9.4% CP diet was fed, cows were randomly assigned to a 2 x 3 factorial where pelleted (P) or unpelleted (UP) soybean meal supplemented corn diets to 12.2% (L), 15.4% (M), and 18.1% (H) crude protein. During depletion, milk production, dry matter intake, and yields of milk protein, fat, and solids decreased in the range of 15 to 25%. However, these all increased to pre-depletion levels after 26 d of repletion. Considering repletion response separately resulted in no significant differences between P and UP for milk production and constituents, feed intake, and plasma urea. However, using depletion to covariably adjust means resulted in P diets favoring greater milk production (P < .01) than UP as well as protein, fat, and solid yields. This response may be caused by a significant increase in feed intake for P diets. Use of a depletion period did increase precision of results but its use in practical feeding trials is controversial. Results in milk, milk protein, fat, and solid yields, and plasma urea were linear with protein level (L vs H). The second trial involved 44 multiparous cows averaging 114 d postpartum. Eight cows remained on a control (CON) diet of 11.7% CP while all others were randomly assigned in a 3 x 3 factorial in which dried (DBG) and wet brewers grains (WBG), and soybean meal (SBM) supplemented the CON to 14.8 (L), 16.3 (M), and 18.0% (H) CP. Diet composition varied in corn silage and ensiled ground-corn but alfalfa silage was constant on a dry matter basis. All diets were superior to CON in milk production and constituent yield. Brewers diets were superior to SBM for milk yield, protein, and solid yields. Part of this response may be related to superior intake for diets containing brewers and lower rumen ammonia and plasma urea. Cows receiving brewers diets have higher intakes than SBM and brewers appear to be utilized more efficiently. For mid-lactating cows an increase in milk at 18.0% CP resulted from brewers diets but not SBM. The H level resulted in a significant increase in milk yield and protein (kg) but also had the highest plasma urea and rumen ammonia level. / M.S.