The interaction between the fluorocarbon surfactant, sodium perfluorooctanoate (SPFO), and beta-lactoglobulin (BLG) was studied. In particular, the effects of cationic surfactants, such as alkyltriethylammonium bromide (CnNE, n = 8, 10, 12), on SPFO-BLG interaction were examined. It was shown that the anionic fluorocarbon surfactant, SPFO, was a strong denaturant of BLG. The ability of SPFO to denature BLG could be weakened by the addition Of CnNE. The effect Of CnNE on SPFO-BLG interaction was related to the hydrocarbon chain length of CnNE, and also the molar ratio of the added CnNE to the SPFO in SPFO-BLG solutions ([CnNE]/[SPFO]). Our findings might provide a way to design surfactant systems that are less denaturing to proteins or tailor the ability of surfactant to denature proteins through the appropriate mixing with other surfactants. (c) 2005 Published by Elsevier Inc.