The interaction of spring wheat dust with human lung airways complement was studied. Airborne spring wheat dust was collected at an active port grain terminal. A water extract of spring wheat dust was prepared at room temperature, and the suspension was poured into a centrifuge tube and rinsed by centrifugation at 5 degrees-C. The interactions of spring wheat dust extract with the human complement system were carried out using human serum in buffered medium. The concentrations of complements in control serum and the endotoxin content of wheat dust were also measured. Spring wheat dust extract exposed serum displayed a considerable drop in concentrations of complements 1, 4, 2, and 3 in this order. The addition of a metal chelator, ethylene-diamine-tetraacetic-acid (60004) prevented the utility of complements 4, 2, and 3; another chelator, ethyleneglycol- bis-(beta-amino-ethyl-ether)-N,N'-tetraacetic-acid (67425) stabilized interactions of complements 4 and 2 and caused a decrease in complement 3. The endotoxin concentrations of the spring wheat dust extract in three samples were 8.87, 17.5, and 4.72 micrograms per milliliter, respectively. The authors conclude that there is more than one pathway in the interaction of human complements with spring wheat dust extracts.