The relaxation processes of excited states in alpha-sexithiophene single crystals have been investigated by femtosecond transient spectroscopy experiments. A vibrational relaxation has been observed during the first 500 fs, leading to the bottom of the lowest Davydov exciton band. Excitons evolve slowly on a subnanosecond scale by bimolecular annihilations to the ground state and by intersystem crossing to triplet states. There is no evidence for the creation of ionized 6T(+) states.