Twenty workers exposed to trimellitic anhydride (TMA) powder an phthalic anhydride (PA) fumes concurrently were evaluated by questionnaire and serum antibody studies. The study group was divided into high-an low-exposure groups on the basis of job descriptions and intensity of daily exposure. The questionnaire, which was designed to identify symptoms compatible with TMA-associated rhinitis, asthma, late respiratory systemic syndrome, and irritant responses, was administered to 18 of 20 workers. Total antibody binding was determined by the ammonium sulfate assay, and specific IgG and IgE binding was measured with an enzyme-linked immunosorbent assay (ELISA) to both PA-human serum albumin (PA-HSA) and TMA-human serum albumin (TM-HSA) conjugates. Specific IgE to TM-HSA was measured with the polystyrene-tube radioimmunoassay (PTRIA). The questionnaire identified nonirritant, immunologic symptoms caused by TMA primarily in the high-exposure group. Specific IgG, IgE, and total antibody binding to TM-HSA and PA-HSA were found exclusively in the high-exposure workers. One worker was identified with PA-associated rhinitis, high total antibody binding, and specific IgG and IgE to PA-HSA by means of the ELISA. The ELISA was as sensitive as the PTRIA in detecting the presence of specific IgE to TM-HSA. The present study demonstrates that an itemized questionnaire, combined with ELISA IgG and IgE determinations, may be a sensitive method for identifying workers who have or are at risk for developing TMA-induced respiratory symptoms.