The substance Arg-Pro-Lys-Pro-(CH2)11CH3 [SP1-4C12] was synthesized by forming a peptide bond between Arg-Pro-Lys-Pro, the N-terminal sequence of substance P and dodecylamine. The aim was to examine the roles of the N- and C-terminal sequences of substance P in stimulating histamine release from mast cells of the rat peritoneal cavity. SP1-4 C12 induces concentration-dependent histamine release in the range 8 to 200 nM. SP1-4C12 was 50 times more potent than substance P and 300 times more potent than dodecylamine. Unlike dodecylamine itself, SP1-4C12 induced noncytolytic histamine release which was inhibited by benzalkonium chloride and by the substance P antagonist [D-Pro4,D-Trp7,9,10]SP4-11. Histamine release induced by SP1-4C12 was inhibited at temperatures below 16 degrees C and did not require the presence of extracellular calcium ions. It is suggested that substance P and some other basic histamine liberators initiate histamine secretion by a mechanism that involves the insertion of a hydrophobic region into the membrane lipid which is necessary to present positively charged moieties to a receptor site involved in activating the secretory mechanism.