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The fluorescence decay of tryptamine and tryptophan in the gas phase was measured in a supersonic free jet. A new technique for producing CW jets of tryptophan in helium was developed in order tocarry out the experiments. The fluorescence lifetimes of several conformers of tryptamine were measured. In each case the fluorescence decay was found to be exponential and the lifetimesfor all conformers were identical (13.2±0.3 ns). In the case of tryptophan, measurements were also made on several conformers. All decays were found to be singleexponential, but in tryptophan, the fluorescence lifetime was found to vary among the conformers. Three conformers had identical lifetimes (12.9 ns), but one conformer had a lifetime of 10.4 ns. The short-lived conformer was the conformer that had previously been observed to produce an emission spectrum containing broad, red-shifted fluorescence. This red-shifted …