The aggregation behavior of N-(2-hydroxydodecyl)-L-alanine (C(12)HAla) and N-(n-dodecyl)-L-alanine (C(12)Ala) was studied in aqueous buffer (pH 12) over a concentration range above their critical aggregation concentration (cac). The C(12)HAla amphiphile has two cacs in contrast to only one cac value for C(12)Ala. The micropolarity and microviscosity of the aggregates were studied by use of pyrene and 1,6-diphenyl-1,3,5-hexatriene, respectively, as fluorescent probes. Dynamic light scattering was used to measure the average hydrodynamic diameter and size distribution of the aggregates. Large size, high microviscosity, and low micropolarity values of the aggregates suggested the formation of bilayer structures in dilute solutions Of C12HAla. In contrast, C(12)Ala was observed to form micelles. Transmission electron micrographs of dilute and moderately concentrated solutions Of C12HAla revealed the existence of spherical vesicles and branching tubular structures, respectively. Comparison of the aggregation behavior of these amphiphiles to that of C(12)Ala and the FT-IR spectrum suggested that intermolecular hydrogen-bonding interactions between adjacent hydrocarbon chains through the -OH and -NH- groups of C(12)HAla are responsible for bilayer formation. The mechanism of nanotube formation was discussed. The temperature dependence of aggregate formation of the amphiphile also was investigated.