We present a theoretical calculation of rates for excited state electron transfer (ET) reactions in zwitterionic tryptophan for each of its six rotameric conformers. Within the Born-Oppenheimer approximation, we calculate the electronic part of the rate, using the renormalized perturbation expansion (RPE) method. The vibrational part is extracted from experimental data, assuming that at neutral pH, the observed fluorescence decay profile is composed of two exponentials corresponding to two competing populations in the sample; one in which fluorescence is accompanied by ET and other that is not. Complementary data, namely, ionization potentials and charge distributions are obtained using a combination of classical molecular mechanics simulation to determine the geometry of the six rotamers, and semiempirical (INDO/S) molecular orbital calculation. Our results indicate that conformers perp chi(2)g(-) and anti chi(2)g(-) give the main contribution to ET in the time scale of fluorescence.