Steady-state emission properties of gossypol in acetonitrile at room temperature have been studied using a HPLC system equipped with a specially improved highly sensitive fluorescence detector (Phi(F) greater than or equal to 10(-7)). The fluorescence lifetimes (tau) have been determined using a time-correlated single photon counting system. At room temperature gossypol shows weak fluorescence with the overall quantum yield of Phi(F) = 5 x 10(-5). On the basis of a comparison of the excitation emission spectra with the absorption spectrum and the radiative properties of gossypol. the origin of gossypol fluorescence from two tautomeric forms: aldehyde in S-1 (n, pi(+)) (tau = 300 ps) and S-2 (pi, pi(+)) (tau = 10 ps) and lactol in S-1 (n, pi(+)) (tau = 18 ps) state was suggested. (C) 2002 Elsevier Science B.V. All rights reserved.