A native grassland, dominated by Agropyron smithii, was continuously fumigated with 2.4 and 7 pphm [parts per hundred million] SO2 mid-May-Oct. 1975 and April-Oct. 1976. Fumigation with SO2 increased the S and ash content of A. smithii. Crude protein content was significantly reduced by 2 yr of SO2 treatment. Dry matter digestibility was significantly lower after 2 yr of SO2 treatment.