To determine the frequency and possible immunologic etiology of respiratory and other symptoms after hog barn exposure, we studied 41 hog farmers and their family members. Participants completed questionnaires and provided serum samples for measurement of IgE and IgG antibodies to hog-derived antigens, hog feed, and hog barn dust. Symptoms after hog barn exposure were reported by 85% of participants. Elevated IgE antibody levels to hog pelt, hog urine, and hog serum were found in only one individual; however, skin tests with these materials were negative. By radioimmunoassay, elevated IgG antibody levels to hog barn dust and/or hog feed were found in seven individuals; two of these sera contained precipitating antibodies to hog barn dust and hog feed. In no case could the presence of IgE or IgG antibodies be correlated with symptoms. Thus it appears that neither IgE nor IgG humoral immune mechanisms mediate respiratory or other symptoms in hog barn workers.