The simultaneous presence of N-acyl-N-methylamide and carboxylate groups in the surfactant molecule produces some unique interfacial properties in aqueous media. These are ascribed to the steric effect of hydrogen bonding between the two groups. Properties of sodium N-dodecanoyl-N-methyl-beta -alanate (SDMA) and N-dodecanoylsarcosinate (SDSa) were compared with those of sodium N-dodecanoyl-N-methyltaurinate (SDMT) and sodium decyloxy-acetate (SDOA) in water in 0.1 M NaCl at 30 C. Evidence for the steric effect on micellization includes the order of increasing A(min) (the minimum area occupied by, the surfactant molecule at the air/water interface) and values of the critical micellar concentration (cmc)/C-20 ratio (a measure of the factors inhibiting micellization relative to adsorption at the air/water interface): SDOA < SDMT < SDSa < SDMA. Evidence for hydrogen-bonded ring formation between the protonated carboxylate group and the amide group includes the same order of increasing pH in the vicinity of the cmc and the greater cmc values by conductance than by surface tension.