Abstract For over 25 years, the high levels of substance P (SP) in primary afferent terminals stimulated speculation that SP might function as a sensory neurotransmitter in the spinal cord 14. Indeed, SP has been closely correlated with the sensory modality of nociception 9; attracting considerable interest to antagonists as potential new analgesics. SP has also been considered for other physiological roles, such as neurogenic inflammation 16. Consequently, the ability to block SP actions is a crucial part of evaluating proposed physiological functions of endogenous SP. Unfortunately, the lack of SP-specific antagonists has been a source of continuing frustration.