The derivatization of saturated long-chain fatty acids (LCFA) with a UV chromophore, 1,4-dibromoacetophenone, using non-ionic micelles to facilitate the reaction is described. Synperonic NP-12 was used as a non-ionic surfactant and tetrakis(decyl)ammonium bromide as an ion-pair agent. The reaction was carried out in the dark at 60°C for 20 min. After adding 1 ml of chloroform to the reaction mixture and centrifugation for 30 s, the mixture was ready for high-performance liquid chromatographic analysis on an RP-18 column. The derivatization rate constant for LCFA was found to be in the range 6 · 10 −4−9 · 10 −4 s −1. The use of micelles overcomes solubility difficulties with highly lipophilic compounds such as LCFA and provides a simple derivatization procedure.