This study compared size-selective workplace protection factors (WPFs) of an N95 elastomeric respirator (ER) and an N95 filtering facepiece respirator (FFR) in agricultural environments. Twenty-five healthy farm workers ranging in age from 20 to 30 years voluntarily participated in this study. Altogether, eight farms were included representing three different types: two horse farms, three pig barns, and three grain handling sites. Subjects wore the ER and FFR while performing their daily activities, such as spreading hay, feeding livestock, and shoveling. Aerosol concentrations in an optical particle size range of 0.7-10 μm were determined simultaneously inside and outside the respirator during the first and last 15 min of a 60-min experiment. For every subject, size-selective WPFs were calculated in 1-min intervals and averaged over 30 min. For the ER, geometric mean WPFs were 172, 321, 1013, 2097, and 2784 for particle diameters of 0.7-1.0, 1.0-2.0, 2.0-3.0, 3.0-5.0, and 5.0-10.0 μm, respectively. Corresponding values for the FFR were 67, 124, 312, 909, and 2089. The 5th percentiles for the ER and FFR were higher than the assigned protection factor of 10 and varied from 28 to 250 and from 16 to 223, respectively. Results show that the N95 ER and FFR tested in the study provided an expected level of protection for workers on agricultural farms against particles ranging from 0.7 to 10 μm. WPFs for the ER were higher than the FFR for all particle size ranges. WPFs for both respirator types increased with increasing particle size.