The presence of colloidal particulates has a significant effect upon the foam fractionation of aqueous solutions of surface-active agents. An experimental investigation is presented of the foam fractionation-flotation of the stannic oxide-cetyltrimethylammonium bromide (CTAB) and stannic oxide-alkyl benzene sdfonate (ABS) systems. The average diameter of the stannic oxide particles was 180A, and particle concentrations were determined by turbidimetry. For stannic oxide-CTAB a froth flotation mechanism controls, and upon foaming feed sols of fixed concentration, fractional residuals of particulates and surfactant are approximately equal. Maximum enrichment ratios are obtained a t maximum aeration time, minimum air rate, and maximum foam height. Increasing the feed concentration of particulates increases the collapsed foam volume, while the CTAB concentration in the residual sol first decreases and then becomes virtually constant. For stannic oxide-ABS sols, no particulates are removed preferentially in the foam. A foam fractionation mechanism controls, and compared with ABS solutions the addition of stannic oxide decreases the foam volume and residual ABS concentration, producing a pronounced increase in the enrichment ratio.