An exciting recent advance in the vanilloid field has been our discovery that resiniferatoxin (RTX), a naturally occurring diterpene combining structural features of the phorbol ester tumor promoters and of capsaicin (see structures in Fig. 1), functions as an ultrapotent capsaicin analog (4—6) and that the esterification of other phorbol-related diterpenes with homovanillic acid at the C-20 position yields synthetic vanilloids of the RTX class with unique spectra of action (7).