The process of heat denaturation of serum albumin, and the properties of several denatured components of albumin were studied using 1-anilino-naphthalene-8-sulfonate as a probe dye. Like native albumin, these protein species all induce fluorescence of the dye with maximum emission at 470 nm when excited at 380 nm. However, the affinity of albumin for the dye decreased on denaturation. This fluorescent dye bound competitively to both native and denatured albumin with another probe dye, 2-(4'-hydroxyphenylazo)benzoic acid, has a specific absorption band at about 480 nm on binding with native albumin. Fatty acids, such as lauric acid, inhibited the interaction of 1-anilinonaphthalene-8-sulfonate with native albumin, but had little effect on its binding with denatured albumin.