The interaction of porphyrins and metalloporphyrins with the monoclonal antibody for meso-tetrakis(carboxy-phenyl)porphine (TCPP) was studied by UV-vis, emission, and circular dichroism (CD) spectroscopy. The UV-vis spectra of TCPP and TCPP-M(Cu, Zn) in the presence of the antibody showed shifts of the Soret bands to a wavelength about 10 nm longer and hypochromicity. The UV-vis and emission spectra of TCPP showed isosbestic points and isoemisive points, respectively, in the presence of various concentrations of the antibody. The spectra of TCPP-Zn showed an isosbestic point in die presence of less than an equimolar amount of the antibody and further increase in the absorption at higher concentrations of antibody, suggesting the existence of a binding mode other than one-to-one binding. The CD spectra of TCPP-M(Cu, Zn) in the presence of the antibody showed strong induced Cotton effects on the Soret band of TCPP-M. The CD spectra of TCPP-Zn with the antibody showed sharp and strong splitting of the Soret band. The CD spectra of TCPP-Cu with the antibody showed a plus-to-minus switch according to the concentration of the antibody. These results suggest the existence of a higher order of association The interactions between the antibody and some other porphyrin derivatives have been studied by spectroscopic methods. The binding modes are discussed.