In two experiments tall fescue (TF) and orchardgrass (OG) were fertilized in split applications on Julian days 107 and 135 with O, 294, or 882 kg NH4NO3/ha and O or 833 kg K2SO4/ha to determine the effect on TF and OG N and S components. Ammonium nitrate fertilization significantly increased total N, nonprotein N (NPN) and protein N (PN) concentrations in TF and OG. Nonprotein N (% of total N) was decreased (P<.001) in TF as level of NH4NO3fertilization increased. Potassium sulfate fertilization did not alter concentration of N components of either grass except NPN concentration was reduced (P<.05) in TF. The NH4NO3level x K2SO4level interaction was nonsignificant for all N fractions. For each grass ammonium nitrate fertilization reduced total S and nonprotein S (NPS) and increased protein S (PS) concentrations significantly while K2SO4fertilization increased all three S components significantly. The NH4NO3level x K2SO4level interactions were significant for all S fractions in TF and NPS and PS in OG. Total N:total S, NPN:NPS and PN:PS ratios significantly increased with increasing level of NH4NO3fertilization in TF and OG. Potassium sulfate application reduced total N:total S ratio significantly in both grasses as well as PN:PS ratio in TF. Herbage total N and NPN concentrations were positively (P<.001) correlated for TF (r = .79) and OG (r = .70). Similarly, correlations between total S and NPS were r = .76 and r = .86 (P<.001) for TF and OG, respectively. Total N and total S concentrations were not related for either grass. These data indicate TF composition was altered by NH4NO3and K2SO4fertilization. Orchardgrass N and S fractions changed as levels of fertilizer NH4NO3and K2SO4were varied.