The adsorption of sodium dodecyl sulfate (SDS) to polystyrene latex particles surface-modified with aromatic amino groups has been examined as a function of surfactant concentration by determination of the particle hydrodynamic radius (RH) using dynamic light scattering. Adsorption isotherms were determined using a surface tension method. At pH 6, without added NaBr, SDS initially adsorbs with the sulfate head interacting with the amino group by hydrogen bonding and with simultaneous contact between the alkyl tail and the polymer chains. The latter leads to aggregation of neighboring polymer chains through bridging by the alkyl tails. Combination of hydrophobic interaction and hydrogen bonding thus leads to an initially strong binding of SDS with the latex surface, resulting in an L-type isotherm. Subsequently, SDS molecules adsorb on the polymer chains by hydrophobic interaction, with the sulfate heads extended toward the solution. Further adsorption occurs about these SDS molecules, and finally globular-like micelles are formed which are anchored on the polymer chains. Added NaBr, even at the 1 mM level, effectively screens the interactions between the sulfate head of SDS and the amino group. Hydrophobic interaction between the polymer chain and the alkyl tail, and also between the alkyl tails themselves, is greatly enhanced. Adsorption isotherms are then of the S type in the presence of NaBr. At high ionic strength an adsorbed monolayer forms at the latex surface rather than as micelles sited on the polymer chains since there is a high density of polystyrene chains at the latex surface. At pH 2, strong electrostatic attraction exists between the sulfate entity on the polymer chain and the amino group. This restricts free extension of the polymer chains and also hinders hydrogen bonding between SDS and the amino groups. SDS will adsorb on polystyrene chains which are anchored in a looped. conformation on the surface, finally forming semiglobular aggregates at saturation. At pH 12, the polymer chain layer at the bare latex surface is strongly compressed. The amino groups associated with OH- ions and the sulfate entities together give a high charge density at the latex surface. Enhanced hydrophobic interaction results on adding electrolyte (base) ions; i.e., the electrolyte promotes SDS adsorption with the alkyl tail in contact with the polymer chain leading to cooperative adsorption of SDS molecules. Electrostatic repulsion between the amino groups, the heads of the adsorbed SDS molecules, and the sulfate entities on the polymer chains extends the polymer chains on which SDS is adsorbed. The extended chains form a suitable steric environment for further SDS adsorption and allow a large adsorbed amount with formation of globular micelles strung along the polymer chains at the cmc. Above the cmc, further adsorption corresponds to growth of the adsorbed micelles. At both pH 2 and pH 12, S-type adsorption isotherms were obtained.