Methylene blue (MB(+)) complexed with guanosine 5’-monophosphate was submitted to subpicosecond (0.8 ps fwhm) laser excitation of wavelength 628 nm, and the decay of the transient difference spectra obtained was analyzed in the 660-840 nm spectral range. The presence of a moderate special shift of the stimulated emission band during the decay was used as an argument for proposing that the strong lifetime shortening of the MB(+) excited singlet (S-1) state in the complex is due to the creation of a double-well structure of the energy surface of the S-1 state by coupling of the locally excited (LE) and charge-transfer (CT) states. Support for this hypothesis was obtained from the observation of a correlation between the S-1 lifetime and the nucleotide oxidation potential for the MB(+) complexes with the 5’-monophosphates of guanosine, xanthosine, inosine, and adenosine, respectively The absence in all these cases of any detectable population of an intermediate state during the decay of the S-1 state shows that the CT state is extremely short-lived. Study of the decay of the transient spectra of the MB(+)-tryptophan complex confirmed the correlation between the Sr-state lifetime and the LE-CT energy gap, In D2O, the S-1 state of the MB(+)-guanosine complex was found to decay more slowly than in H2O. This result was interpreted as a dynamical solvent effect characteristic of LE --> CT transitions.