The interaction of cationic surfactants such as CTAB (cetyl trimethyl ammonium bromide) with tetrakis-(4-sulfonato phenyl) porphine (H 4 TPPS 2ร ), a dianion, leads to the formation of two premicellar aggregates of porphyrin when [CTAB] is below CMC (critical micelle concentration) and a micellized monomer when [CTAB] is above CMC. The premicellar aggregates are labeled as J-and H-aggregates because of their characteristic spectroscopic properties. Simple inorganic cations such as K , Ba 2 , Ca 2 and Zr 4 also induce the formation of the J-aggregate but not of the H-aggregate. The formation of the J-aggregate is preceded by kinetic intermediates, while no intermediate was observed prior to the formation of the Haggregate. The rate of formation of the H-aggregate was faster than that of the J-aggregate. The fluorescence depolarization (anisotropy) properties of the monomer and the H-and J-aggregates were studied and compared. The size and structure of the J-aggregate were examined by transmission electron microscopy (TEM). The structure of the J-aggregate reveals a fiber-like (linear stacking) or domain-like (helical stacking) arrangement of the porphyrin molecules.