A new system has been developed to determine the workplace protection factors (WPF) for dust and bioaerosols in agricultural work places. The study was performed with a person wearing an N95 filtering facepeice respirator while doing typical farm tasks such as feeding animals, harvesting grain, unloading grain, and facility investigations. Results showed that the particle size increased along with the geometric means. The WPF for total cultural fungi was greater than for total culturable bacteria. Among the different microorganism groups, the WPFs of Cladosporium, culturable fungi, and total fungi were significantly correlated with the WPFs of particles of the same sizes. When the WPFs for dust particles was compared to the WPFs for bioaerosols it was found that the bioaerosols were below 10 more frequently, which is a recommended assigned protection factor (APF). Over half of the WPFs for microorganisms were below the proposed APF of 10. The APF of 10 for an N95 filtering facepeice respirators seems inadequate against microorganisms. This study provides preliminary data to establish guidelines for respiratory protection against airborne dust and microorganisms on typical farms.