A study of the quality of respirator protection and acceptability among agricultural workers was conducted. The cohort consisted of 50 workers involved in swine production, 20 persons employed on poultry farms, 46 persons working at grain handling sites, and 12 persons involved in silo uncapping and unloading operations on dairy farms. They wore a variety of respirators and powered air purifying (PAP) helmets during their work. Total airborne dust and endotoxin concentrations were measured in workplace ambient air and inside respirators. Workplace protection factors (WPFs) for the respirators were computed. The grain handlers and poultry and swine production workers completed a questionnaire to rate overall comfort (acceptability) and factors contributing to acceptability of the respirators. Geometric mean (GM) total dust and endotoxin concentrations in the workplace air ranged from 3.75 to 136mg/m3 and 4.1 to 8.2 endotoxin units per cubic meter (EU/m3). The highest dust and endotoxin concentrations were measured during the silo uncapping operations at the dairies. The GM dust endotoxin contents varied from 31.5 to 85.2EU/mg, the highest concentrations occurring in the swine production facilities. The WPFs of the disposable respirators, quarter and half masks, and PAP helmets averaged 13, 22, 19, and 30, respectively. The poultry production workers rated the PAP helmet to be the most acceptable. The grain handling workers preferred the half mask and the swine production workers judged both the quarter and half mask to be the most acceptable. For ease of breathing and communication, skin comfort, and in/mask temperature and humidity, the PAP helmets were rated best overall and the disposable respirator and half mask the worst. For weight and convenience of use, the disposable respirators were rated best and the PAP helmets worst. The authors conclude that the measured WPFs of the examined respirators are generally lower than those measured in laboratory studies, but comparable to those measured in other field studies. User acceptability varies with respiratory type.