Résumé : Background: Substance P (SP) is a neuropeptide transmitter found in sensory neurons of the central nervous system and related to pain sensation and respiratory regulation. Some reports claim an increase in SP in the brains of SIDS victims, so the correlation between SP and sleep apnea was investigated here. Materials and methods: Among 27,000 infants studied prospectively to characterize their sleep-wake behavior, 38 infants died under 6 months of age, which included 26 cases of sudden infant death syndrome (SIDS). All the infants had been recorded during one night in a pediatric sleep laboratory some 3-12 weeks before death. The frequency and duration of sleep apnea were analyzed. Brainstem material was collected and immunohistochemistry for SP was carried out. The density of SP positive fibers was measured in the nucleus spinal and mesencephalic nervi trigemini and nucleus parabranchialis in the brainstem of abovementioned cases. Correlation analyses were carried out between the density of SP and the data of sleep apnea. Results: There was no SIDS specific correlation of SP through the above-listed parts of the midbrain with frequency and duration of sleep apnea. Conclusions: There was no significant association between the SP findings and apnea data in SIDS; this is not in agreement with the association of apnea in pathophysiology of SIDS. © 2004 Elsevier Ireland Ltd. All rights reserved.