Pulse radiolysis has been used to examine scavenging of hydrated electrons (e(aq)(-)) by 3,3’-dimethylbiphenyl (DMBP) and hexadecylpyridinium chloride (HPCl) in anionic micellar solutions of sodium dodecyl sulfate (NaDS) in the presence of the electrolytes with tetramethyl- and tetrabutylammonium cations (TMA(+) and TBA(+), respectively) and, for comparison, in NaDS/NaCl solution. The obtained kinetic data for e(aq)(-) and the absorption spectra and decay of the radical-anion DMBP(.-) are discussed, taking into account location of the scavengers in micelles and electrostatic and structural effects of added counterions. It is concluded that the DMBP molecule is embedded below the head-group region, while the pyridinium ring of the HPCl molecule (the reactive center) remains anchored on the micellar surface. The hydrated electron does react with the surface-located acceptor, in spite of electrostatic repulsions between e(aq)(-) and the aggregates. The rate constant of the reaction, ca. 7 times lower in neat NaDS than in homogeneous aqueous solution, increases versus concentration of the added electrolyte; the effect is much more pronounced in the presence of hydrophobic tetraalkylammonium counterions than in the presence of hydrophilic Na+. Micellized DMBP is not accessible for hydrated electrons in neat NaDS and in NaDS/NaCl solutions at [NaCl] less than or equal to 0.3 M. The reaction becomes possible, however, with addition of TMA(+) and TBA(+) counterions. The observed specific effect of tetraalkylammonium counterions on the reactivity of e(aq)(-) toward micelle-bound scavengers indicates a more disordered structure of the surface region of the aggregates due to intercalation of the hydrophobic cations between surfactant heads, in accord with the structural model of sodium and tetramethylammonium dodecyl sulfate micelles inferred earlier from the studies by ESR and ESEM methods.