Hymenolepis diminuta infection can initiate a nonmigratory contractile pattern of the small intestine, called the sustained spike potential (SSP). These contractions slow the movement of material along the length of the small intestine. In the absence of a tapeworm infection, the SSP can also be induced by infusion of the cyclic nucleotide, cyclic guanosine monophosphate (cGMP), into the duodenum of a rat. cGMP induces the SSP pattern of contraction in a dose-dependent fashion. The intestinal infusion of at least 200 nmol of cGMP alone is required to induce SSP. The infusion of succinate and cGMP together, effectively lowers the minimal-necessary concentration of cGMP required to induce SSP by 1 × 10⁶ times. Succinate alone does not induce SSP; however, succinate acts cooperatively with cGMP, allowing the stimulation of SSP with as little as 560 fmol of cGMP. The amounts of succinate (2.4 μmol) and cGMP (560 fmol) in 0.2 ml infused in this study are the amounts reported by earlier studies to be present in 0.2 ml of H. diminuta–conditioned medium. This indicates that succinate and cGMP, 2 secretions from the tapeworm, interact with the tissues of the small intestine to activate an SSP pattern of contractility.