Hyper-Raman scattering of all-trans-retinal was measured for the first time in solution at room temperature. Under the two-photon resonance condition, the intensity of hyper-Raman scattering was so strong that it could be measured from a diluted solution at a concentration as low as I x 10(-3) mol dm(-3). Hyper-Raman excitation profiles were examined in the excitation wavelength range from 770 to 840 nm (lambda(ex)/2, 385-420 nm). In this excitation range, the intensity of all the hyper-Raman bands monotonically increased with shortening excitation wavelength, and the hyper-Raman spectral feature was very similar to that of resonance Raman spectra excited with double the excitation energy (lambda(ex)/2). The resonance mechanism of hyper-Raman scattering was discussed, and it was concluded that hyper-Raman scattering gains intensity enhancement from a two-photon resonance with the "B-1(u)*" state, not with the "'(1)A(g)*" state, through the Franck-Condon (the A term) mechanism.