Abstract A fluorescence method was applied to study structural transitions occurring in the ternary system lecithinsodium deoxycholate-water. The method is based on binding of the hydrophilic probe rhodamine-B to the structures at molar ratios of lecithin and deoxycholate ( L/D) ranging from 0.16 to 10.7. The relationship between the fluorescence intensity and L/D ratio was sharply altered at molar ratios of 0.9 and 4.5. Thus three L/D regions could be distinguished and inflection points were estimated for each one. It is suggested that the L/D values of the sharp transitions (0.9 and 4.5) and the inflection points (0.5, 1.5 and 5.5) indicate generation of new types of molecular arrangements in the ternary system.