We conducted a prospective study of 63 patients resuscitated from cardiopulmonary arrest (CPA) to analyze the prognostic significance of changes in brainstem reflex activity. Brainstem reflex abnormalities were common in the early postresuscitation period. Among survivors, reflexes returned to normal within 48 hours. Reflex abnormalities were significant predictors of poor outcome by 6 hours after CPA. No survivor had absent pupil light or corneal responses from 6 hours after CPA, and loss of reflex response after this time occurred in only one survivor.