Results are presented of field determinations of effectiveness (workplace protection factor; WPF) and acceptability (questionnaire responses) by respirator users in indoor swine production, poultry production, and grain handling facilities. Dust mass and endotoxin in air samples collected over 4 hours outside the mask and inside the mask were compared to yield the WPF. Disposable respirators had a mean WPF of 13; quarter-mask respirators, 22; half-mask respirators, 19; and powered air purifying helmets, 30. These values are generally less than laboratory-based measures of effectiveness but similar to other field data. Acceptability among these four classes of respirators varied among the three user groups: poultry operators preferred the powered helmet; grain handlers preferred the half-mask; and swine producers were split between the quarter-mask and half-mask respirators. Fully disposable masks were preferred by only 20 to 22 percent of the workers in each setting. Among all groups of workers, powered helmets were rated best for breathing ease, communication ease, skin comfort, and in-mask temperature and humidity, while disposables were rated best for weight and convenience. However, in all but one of the above acceptability characteristics, the opposite respirator was given the worst rating. Thus, the reusable quarter-mask or half-mask is most often the best compromise.