This is a report of 46 employees exposed to trimellitic anhydride (TMA). The evaluation consisted primarily of periodic serum antibody studies and a questionnaire that identified symptoms compatible with allergic asthma and/or rhinitis, late respiratory systemic syndrome (LRSS), or pulmonary disease anemia (PDA) syndrome. Industrial hygiene data from the plant in 1989 reported exposures that were lower than levels in 1979. Seven employees had positive IgE antibody against trimellityl-human serum albumin (TM-HSA); one had TMA rhinitis, and another possibly had TMA asthma/rhinitis. Fourteen employees had positive IgG antibody against TM-HSA of whom only three had titers high enough to cause disease, and none of them had symptoms compatible with LRSS or PDA. At most, two workers had asthma or rhinitis during the 1990 evaluation. In summary, in this employee population with low level TMA exposure there is a low incidence of immunologically mediated disease due to TMA.