The effectiveness of a dust control technique during chopping of bales of hay and straw was measured. Eight dairy farms New York were sampled, each over a 2 day period. On day one, measurements were made during normal bedding chopping. On day two, 1 quart of water was added to the cut side of each bale before chopping, during which sampling was performed. Other variables were kept constant throughout the samplings. Gravimetric particulate measurements were made on sampled air drawn by an inhalable like sampler. Photometric particulate measurements were made using Miniram aerosol monitors. Particle size distribution was determined using a cascade impactor. Air samples were drawn through cellulose-ester and polycarbonate filters, and the filters were examined by a variety of microscopic techniques. Endotoxin was measured using a modification of the Limulus amebocyte lysate test. Histamine was measured by radioimmunoassay. Area samples were tested for microorganisms. Direct reading measurements for carbon-monoxide (630080) were made on the chopper operator. Personal and area measurements of dust, endotoxin, and histamine showed substantial reductions when the dust control method was used. Dust and endotoxin decreased five fold, while histamine decreased over ten fold. Measurements of bacteria, fungi, and gross microscopic examination of air samples showed significant improvement in quality. Both wet and dry treatments resulted in no difference in carbon-monoxide levels, with both occasionally showing levels well above the ceiling value of 200 parts per million, indicating the need for improved ventilation or an alternative power source. The authors conclude that applying water to the bales is an effective method of dust reduction.