1. Mechanical or electrical stimulation of isolated sections of body wall produced contractions that were graded with the intensity of the stimulus. Injury of body wall with shallow incisions produced extremely persistent contractions. 2. Long-lasting contraction of isolated body wall was also produced by brief application of "stimulated body wall wash" (SBW), sea water which was first washed through another section of body wall subjected to intense mechanical or electrical stimulation. Contractions were produced by SBW diluted to concentrations as low as 1% of the initial concentration. Contractions produced by prolonged application of SBW showed little fatigue, tachyphylaxis, or desensitization. 3. SBW caused contraction of isolated sections of body wall from all regions of the body, including tail, parapodia, siphon, purple gland, rhinophores, and anterior tentacles. SBW also caused contraction of isolated lateral columellar muscle and of the gill. 4. 30 mM CoCl2 blocked the release of contractile factors into electrically stimulated body wall and reduced but did not abolish contractile responses of unstimulated body wall to perfused SBW. SBW contractions were unchanged by disconnection of the perfused tissue to the CNS. 5. Hemolymph collected from the neck of an intact donor following strong electrical stimulation of the tail or excision of a parapodium ('stimulated hemolymphh, SHL) caused long-lasting contractions which were larger than those produced by control hemolymph (CHL) collected prior to stimulation of the donor. 6. Similarities between body wall contractions produced by SHL and by SBW, including their occurrence in 30 mM CoCl2, suggest that some of the contractile activity in SHL may be directly released from traumatized body wall. 7. SHL caused significantly greater cardioacceleration of the isolated heart than did CHL. Similarities between the cardioacceleration produced by SHL and by SBW suggest that a source of cardiac activity in SHL may be traumatized body wall. 8. SBW suppressed the gill-withdrawal reflex when applied selectively to the sheathed or desheathed abdominal ganglion. SBW-induced suppression was associated with significant reduction of evoked spike activity in identified gill motor neurons. SHL collected 1-2 h after noxious stimulation caused weak but significant suppression of the gill-withdrawal reflex when applied to the fully sheathed abdominal ganglion.