Widespread acceptance of a definition of pain that focUseson pain perceptionhas led, directlyor indirectly, to many recent advances. Important classificationsof pain syndromes, the framework for diagnostic categories, and the resultant search for effectivetreatments havebenefitedfrom definingpain as a subjectiveexperience. Seminaladvances in the mechanismsof chronic~,@ mmhdation, its phenomenology, contextual influences, andnoveltherapeuticapproacheswouldnot haveowurred if the deftition of pain was limitedby the omurrence of a proximate stimulus (Von KorfYet al. 1992; Merskeyand Bogduk 1994). Investigationof the widelyvariableneural elementsand physiologicprocesses involvedin the integration, processing, modulation of incomingnociceptiveinformation at ditTerentlevelsof the CNS and within difYerenttime framescan also be related to the present deftition (Anand and Carr 1989; Abram 1993).

In its present form, however, the definition of pain challengesour understandingof pain becauseit does not apply to living organisms that are incapable of selfreport. This includesnewborn and older infants, small children, mentally retarded, comatose, demented, or verbally handicapped individuals, and all primate and non-primateanimals. For the purposesof this editorial, wewillassumethat the operationalconsequencesof this definitionare most evidentin the clinicalcare givento