A good condition, tallgrass prairie experimental area was treated with selected combinations of atrazine, 2,4-D, and NPK fertilizer in spring 1975 and 1976. Crude protein contents in November herbage ranged from 3.401, to 6.3% in treated samples. Untreated herbage contained 5.0% crude protein. Nonlactating beef cows were allowed to graze freely on the area during December, 1976. Utilization of herbage ranged from 43% to 87%. Utilization was greatest on NPK areas (82%), 3.4 kg atrazine + NP areas @SO/O), and 3.4 kg atrazine-I-NPK areas (87%). Decreaser species comprised a larger percentage of the total production on atrazine i-NP, atrazine-I-NPK, and 2,4-D-I-NPK areas than on fertilizer-only areas. Tallgrass prairie treated with atrazine and fertilizer or 2,4-D and fertilizer was preferred by beef cows as winter forage over untreated herbage. There was a 15% increase in herbage utilization for every 1% increase in crude protein in the herbage in December.