The purpose of this study was to determine whether workers sensitized by one acid anhydride, trimellitic anhydride (TMA), would possibly react immunologically to two other acid anhydrides, phthalic anhydride (PA) or maleic anhydride (MA). We studied serum samples from four workers with TMA asthma and immunoglobin E (IgE) against TMA conjugated to human serum albumin (TM-HSA). In enzyme-linked immunosorbent assay (ELISA) cross-inhibition studies, TM-HSA inhibited IgE binding to TM-HSA, but when 100 times more P-HSA or M-HSA was used, no significant inhibition occurred. However, in ELISA studies of P-HSA and M-HSA, we saw binding of specific serum IgE. Finally, in passive transfer studies in rhesus monkeys with serum from an individual with antibodies to all three acid anhydrides, the following titers were obtained: TM-HSA (1:32), P-HSA (1:8), M-HSA (negative). We conclude that cross-inhibition studies may not be the best method for determining whether an individual sensitized to one antigen will react to a related antigen. The determination of biologic reactivity in a rhesus monkey model of passive cutaneous transfer makes it likely that biologic reactivity would also occur in a human sensitized to TMA and then exposed to another anhydride such as PA.