The induction of aggregate formation of cationic polysoaps ((CL)-Copol C1-12), cetyltrimethylammonium bromide (CTAB), n-dodecyltrimethylammonium bromide (DTAB), and n-dodecylmethyldiallylammonium bromide (DMDAAB) by low concentrations of Methyl Orange (10(-5)-10(-4) M) and anionic surfactants (concentrations below their cmc’s) in aqueous solutions was studied using UV-vis absorption and fluorescence spectroscopy. Reduced viscosities were also investigated as a function of polysoap concentration in the presence of low concentrations of the same additives. It was found that the cationic polysoaps, CTAB, DTAB, and DMDAAB aggregate far below their normal cmc in the presence of Methyl Orange in aqueous solution. The cationic polysoaps exhibited an about 5-fold decrease of the reduced viscosity in the presence of the hydrophobic anionic additives but no decrease of the reduced viscosity was found in the presence of hydrophobic nonionic additives and cationic additives (CTAB, DTAB). Depending on the length of the alkyl chains of the organic anionic additives, a conformational transition of the cationic polysoaps was indicated by changes of the reduced viscosity. Pyrene was used as a fluorescence probe to investigate the conformational state of the cationic polysoap CL-Copol C1-12 in the presence of low concentrations of additives. Pyrene fluorescence spectra revealed the formation of hydrophobic microdomains in the presence of the hydrophobic anionic additives depending on the length of alkyl chains. These domains were not observed in the case of hydrophobic cationic additives and nonionic additives.