The fluorescence characteristics of 7-anilino-4-methylcoumarin-3-acetic acid (AMCA), which may be useful as a fluorescent probe in protein binding investigations, were examined in various solvents and α-globulin solution. The fluorescence of AMCA was significantly enhanced in lesspolar solvents and in the presence of α-globulin with a shift of the emission maximum to shorter wavelength. Scatchard plots and continuous variation plots indicated that one molecule of AMCA binds to α-globulin. AMCA was applied as a probe in binding studies of some estrogens and corticoids with α-globulin. The spectral changes of the AMCA-α-globulin system in the presence of steroids indicated that estrogens (α- and β-estradiol, estriol) competitively displace AMCA bound to α-globulin but corticoids (cortisone, hydrocortisone) do not. The binding parameters of estrogens for α-globulin were also estimated. The present data suggest that AMCA is useful as a fluorescent probe for assessing the binding of steroids, including estrogens, to α-globulin.