The goal of this study was to compare the behavior of structurally homologous local anesthetics (LAs) adsorbed to a simplified membrane model. Interactions of LAs with micelles made from negative and neutral detergents were assayed by drug fluorescence. Micellar:drug affinity, equivalent dielectric constant and pKa of bound LAs were assessed for procaine, tetracaine, procainamide, benzocaine and aminoparabenzyldiethylamine, a procaine homologue containing an alkyl chain instead of an ester bond. Shifts in maximum emission wavelength and changes in fluorescence intensity showed that 1) increased LA hydrophobicity (expressed as octanol:buffer partition coefficient) corresponded to increased affinity for all micelles; 2) protonated species of LA were bound more tightly than neutral species to negative micelles, but less tightly to unchanged micelles; 3) drugs with larger dipole moments (amide < ester < alkyl) bind less tightly to micelles than those with smaller dipoles; 4) Larger dipole moments of LAs also result in a larger equivalent dielectric constant around the micellar-bound LAs, meaning that the LA binds at a shallower depth from the micelle surface; and 5) binding the neutral micelles lowers the pKa but binding to negatively charged micelles raises the pKa (due to the concentrating effects of surface charge on H+). The results provide a picture of interfacial adsorption of LAs in a relatively simple system that should allow interrelation of the dipole field contributions to LA behavior in phospholipid bilayers.