Formation of covalently bound protein adducts with 2-arylpropionic acids (2-APAs) has been proposed as a possible explanation for hypersensitivity and toxic responses to chiral carboxylic acid drugs. To identify the cellular proteins chemically modified with optically active (S)-ibuprofen, we generate polyclonal antibodies by immunizing rabbits with immunogen coupled to bovine serum albumin (BSA) via the spacer of 4-aminobutyric acid. The resulting antibodies largely cross-reacted with N-alpha-(t-butoxycarbonyl)--(S)-ibuprofenyl lysine as well as with the conjuguated (S)-ibuprofen with glycine and taurine and unconjugated (S)-ibuprofen, enabling enantioselective detection of (S)-ibuprofen residues anchored on ovalbumin molecules, introduced by the reaction of the ibuprofen p-nitrophenyl ester. Furthermore, immunoblotting with an antibody allows the enantioselective detection of (S)-ibuprofen-introduced glutathione-S-transferase (GST). These results indicate that the developed method will be useful for monitoring the generation and localization of protein covalently bound with (S)-ibuprofen, which may be the cause of ibuprofen-induced toxicity.