Covalently bonding multiple fluorine atom tags to the precursors of monoamines could provide compounds for functional imaging. Theoretically, the fluorine atoms can produce detectible signal if concentrated in vesicles inside neurons. Prior to committing more costly resources to the project, evidence was sought for uptake of the molecules into neurons in living organisms. Two 19F tag configurations of seven or nine atoms were investigated. Crayfish aggression provided a paradigm for obtaining preliminary data on the scarce new molecules. After establishing that 5-hydroxytryptophan (5-HTP) elicited serotonin-like effects, the fluorine tagged versions (PF-5-HTP) were investigated; then, the elevated aggression produced by these precursors to serotonin was blocked by coadministering fluoxetine. Treatment order effects and interrater reliability of the behavioral inventory were evaluated. Preliminary evidence that these imaging compounds are taken up into neurons obtained by studying crayfish behavior later found support using more sophisticated neuroscience techniques.