Dead-end flow membrane filtration was run in an Amicon 8500 cell. Sheet membranes of cellulose acetate and polysulfone, cut-off 15-30 kDa, effective surface area 13.4 cm(2), were used. Dyes and surfactants concentrations were 0.1 g/l. and 1.84 mM, resp. Anionic dyes (MO, OR 11, DB-0, CR, and 3RL) were examd. in classical ultrafiltration (UF) and in micellar-enhanced OF (MEUF) in the presence of hexadecyltrimethylammonium bromide (CTAB). Classical OF enabled only M > 600 dyes to be sepd..(retention 99%; at M < 600, 25-65%). The M < 600 were sepd. by MEUF in 99%. Again, MEUF enabled log(micellar binding const.), micelle loading, and distribution coeff. to be detd.