A four-region model based on electrostatic and hydrophobic interactions adequately explains adsorption of anionic surfactants on positively charged solids such as alumina. In this study, cationic surfactants were used instead for adsorption on negatively charged alumina at pH 10 and at a constant ionic strength of 0.03 M NaCl. In this case, only three distinct regions were observed in the adsorption isotherms and there seemed to be a lack of adsorption region III. In order to elucidate the adsorption mechanisms involved, the electronic spin resonance and fluorescence techniques were used along with vacuum flotation technique. The results suggest that adsorption region III may still exist; the difficulty in detecting it from the adsorption isotherm is probably the result of similar slopes for regions II and III. And this may be attributed to the loose and interpenetrating solloid structure in the case of the cationic amine/negatively charged alumina system. This possibility is discussed with the help of the results of the spectroscopic and flotation studies.