The mass spectra of the four tryptamine derivatives, N-acetyl-5-methoxytryptamine (melatonin), N-acetyl-5-hydroxytryptamine (N-acetyl-serotonin), N,N-dimethyl-5-hydroxtryptamine (bufotenine) and N,N-dimethyl-5-methoxytryptamine (O-methylbufotenine), with specifically labeled [D4] aminoethyl sidechains have been measured. Comparison of these spectra with those of the unlabeled compounds enable the major fragmentations of the compounds to be defined.