Large, colorless aggregates are observed during the induction period of a chemical oxidative polymerization of aniline in, dilute aqueous acids using an ammonium peroxydisulfate oxidant. Observed for the first time by static and dynamic light-scattering (LS) measurements, these aggregates are believed to be anilinium-peroxydisulfate ion clusters whose shape (spherical or rodlike) plays an important role in the overall morphology of the emeraldine salt formed (granular or fibrillar). The role of these I aggregates in influencing the morphology of polyaniline is further evaluated under a variety of reaction conditions, for example, varying ionic strength, concentration, temperature, nitrogen substitution, and so forth.