OBJECTIVES: The sensitizing properties of organic acid anhydrides (OAA) were evaluated in a rat model. METHODS: The development of specific immunoglobulin (Ig)E and Ig G in serum was investigated after immunization with 14 OAA and 3 OAA conjugates. Brown Norway rats were injected intradermally with 0.1 ml of 0.2 M OAA in liquid paraffin or 1.4 mg of rat serum albumin conjugate in saline. Serum samples were collected after 4 weeks. Antibodies were analyzed with enzyme-linked immunosorbent assay. RESULTS: The serum titers of specific Ig E after immunization with the different free OAA varied from