Immunological and respiratory findings were studied in a group of 19 male soy-bean workers. A group of 31 control workers were examined for the prevalence of respiratory symptoms and 20 control workers were included in the immunological study. All soy-bean workers had positive immediate skin reaction to soy-bean dust, 18 to soy antigen after separation from oil, three to lecithin antigen and only one to soy oil. Only three soy-bean workers had increased levels of specific IgE. Among 20 control workers, 19 reacted to soy-bean dust, 20 to soy after separation of oil and none to soy oil. One demonstrated increased specific IgE. The prevalence of chronic respiratory symptoms was considerably higher in exposed than in control workers, being statistically different for dyspnea (P less than 0.01). The statistically significant acute reductions in ventilatory capacity were particularly pronounced for FEF50 (-4.7%) and FEF25 (-9.4%). The mean ventilatory capacity values before shift on Monday were significantly lower than those on the following Friday for FVC, FEF50 and FEF25. There was no difference in ventilatory capacity between soy-bean workers with positive and those with negative skin tests to house dust or between those with increased and those with normal IgE serum levels. A water soluble extract of soy-bean dust was also assayed in organ bath containing guinea pig trachea. This model showed the extract to be highly reactive causing a dose-related constriction of airway smooth muscle. Our data suggest that immunologic sensitization to soy-bean products is very frequent. In addition to possible humoral contribution to respiratory disorders, soy dust seems to directly affect airway smooth muscle.