Two-photon absorption cross sections of two dye molecules, doped in thin films of polymethylmethacrylate, are measured by comparing fluorescence intensities induced by single- and two-photon excitations. Ratio of the single- and two-photon absorption cross sections is related to the ratio of the single- and two-photon pumped fluorescence intensities. Using this sensitive and background-free detection technique, dispersion of the nonlinearity is measured over a wavelength range of 700–800 nm. ©1997 American Institute of Physics.