Application of a neuropsychological model, developed in the laboratory, to the graffiti of Tikal reveals that the great majority of the latter are products of altered states of consciousness, depictions of visions seen by people in states of trance in relatively private settings. Beneath this art's apparent surface disorder and haphazard arrangement lies a definite neuropsychological order. Consideration of the provenances of graffiti suggests that the practice of trancing was widespread in Classic times, at least among the elite class and upper stratum of commoners.