Calea zacatechichi is a plant used by the Chontal Indians of Mexico to obtain divinatory messages during dreaming. At human doses, organic extracts of the plant produce the EEG and behavioral signs of somnolence and induce light sleep in cats. Large doses elicit salivation, ataxia, retching and occasional vomiting. The effects of the plant upon cingulum discharge frequency were significantly different from hallucinogenic-dissociative drugs (ketamine, quipazine, phencyclidine and SKF-10047). In human healthy volunteers, low doses of the extracts administered in a double-blind design against placebo increased reaction time and time-lapse estimation. A controlled nap sleep study in the same volunteers showed that Calea extracts increased the superficial stages of sleep and the number of spontaneous awakenings. The subjective reports of dreams were significantly higher than both placebo and diazepam, indicating an increase in hypnagogic imagery occurring during superficial sleep stages.