Seizures, brain swelling, and cortical necrosis have been observed in the newborn rhesus monkey following a 2 to 4-hour period of intrauterine partial asphyxia produced by halothane-induced maternal hypotension. These clinical and neuropathologic findings are similar to those seen in human newborn infants who have experienced an episode of intrauterine asphyxia from such a cause as premature placental separation. The present study strongly indicates that fetal partial asphyxia, from any cause, in the absence of fetal circulatory collapse or fetal head compression, may be the primary event that sets in motion a vicious cycle of brain swelling and impaired cerebral blood flow, leading finally to cerebral necrosis.