Conductivity (kappa), turbidity (tau), and fluorescence (I-1/I-3) studies of hexadecyltrimethylammonium bromide (HTAB), hexadecylpyridinium bromide (HPyBr), and hexadecylpyridinium chloride (HPyCl) in aqueous poly(amido amine) (PAMAM) dendrimers of generations 0 to 2.5 G have been carried out. The complexation of surfactant monomers with the PAMAM surface groups is demonstrated by the critical aggregation concentration (cac), which is two to three orders of magnitude less than the micellization of cationic surfactants in aqueous PAMAM and denoted by critical micelle concentration (cmc*). In the presence of aqueous amine-terminated PAMAM, the cmc* value for each surfactant was much lower than the cmc in pure water, while they remain close to each other in the presence of aqueous ester-terminated PAMAM for each surfactant. The fluorescence studies demonstrated that both amine- and ester-terminated PAMAM interact with the cationic surfactants, though the mode of interaction varied due to the different nature of surface groups. (C) 2004 Elsevier Inc. All rights reserved.