1 The effects of substance P and related peptides on amylase release from rat parotid gland slices have been investigated. 2 Supramaximal concentrations (1 microM) of substance P caused enhancement of amylase release over the basal level within 1 min; this lasted for at least 40 min at 30 degrees C. 3 Substance P-stimulated amylase release was partially dependent on extracellular calcium and could be inhibited by 50% upon removal of extracellular calcium. 4 Substance P stimulated amylase release in a dose-dependent manner with an ED50 of 18 nM. 5 All C-terminal fragments of substance P were less potent than substance P in stimulating amylase release. The C-terminal hexapeptide of substance P was the minimum structure for potent activity in this system, having 1/3 to 1/8 the potency of substance P. There was a dramatic drop in potency for the C-terminal pentapeptide of substance P or substance P free acid. Physalaemin was more potent than substance P (ED50 = 7 nM), eledoisin was about equipotent with substance P (ED50 = 17 nM), and kassinin less potent that substance P (ED50 = 150 nM). 6 The structure-activity profile observed is very similar to that for stimulation of salivation in vivo, indicating that the same receptors are involved in mediating these responses. 7 All the fragments of substance P tested were capable of eliciting a full amylase release response. This indicates that the apparent partial agonist action of the C-terminal nonapeptide fragment on in vivo salivation is not explicable at the receptor level.