A longitudinal study of workers involved in the manufacture of trimellitic anhydride has been in progress since 1977. Trimellitic anhydride is a low-molecular-weight, reactive chemical used in the manufacture of plastics. Initial studies done in 1976 defined three syndromes due to inhalation of trimellitic anhydride: asthma-rhinitis, a late respiratory systemic syndrome, and an irritant response. Also, serologic techniques were developed to measure total antibody and IgE antibody to trimellityl human serum albumin. From 1977 to 1981, 64 workers were assessed. Six workers presented with asthma-rhinitis, high levels of IgE antibody, and skin test reactivity to trimellityl human serum albumin; five workers developed the late respiratory systemic syndrome; and one worker had both immunologic syndromes. These serologic measurements detected or were predictive of an immunologic respiratory illness and were useful in monitoring workers involved in the manufacture of trimellitic anhydride.