Using myoelectric recording techniques, we examined the myoelectric effects of castor oil; ricinoleic acid (cis isomer), the active ingredient of castor oil; and ricinelaidic acid (trans isomer) in the small intestine of New Zealand white rabbits. Ricinoleic acid, 2 microgram/kg per min (6mM), was perfused into a distal 12-cm ileal loop. An abnormal myoelectric pattern developed that was similar to the alteration in the electrical activity that has previously been reported for cholera enterotoxin. Castor oil, 0.85 ml/kg, had a similar effect. Ricinelaidic acid, 2 microgram/kg per min, induced no activity. A second preparation consisted of an intraluminal perfusion of ricinoleic acid, 2 microgram/kg per min, into the first section of the duodenum. The abnormal myoelectric pattern was observed in the jejunum and the ileum but not the duodenum. The mean onset time for the development of this altered myoelectric state for all experiments was 3.5 h. These studies suggest that an active motility component in addition to the secretory state exists throughout the small intestine that is exposed to castor oil or ricinoleic acid.