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Abstract— –Fluorescence decay times of aqueous dilute solutions (˜20 µM) of L‐tryptophan have been determined using the phase shift technique as well as single photon‐counting coupled with synchrotron radiation (ACO at Orsay and SPEAR at Stanford). Decay times were obtained as a function of the excitation wavelength (in the spectral region 220–320 nm) monitoring emission of λ> 320 nm (in certain specified cases, λ> 360 nm). We have found that, at neutral pH and 20°C. fluorescence decays are single exponentials and independent of the excitation wavelength; under these conditions we find τ= 3.1 ± 0.1 ns.