Management of 50 experimental newborn infants ill with narcotic withdrawal has been carried out with the aid of an instrument developed for measuring its severity, the Neonatal Narcotic Withdrawal Index (NNWI). With its use, infants exposed to methadonein uterohave been successfully cared for with detoxification needed in less than 25% of cases and for durations of less than 2 weeks. The percentage of cases and the length of treatment is much less than is customary for infants who have been prenatally exposed to similar doses of methadone. Validity of the NNWI is shown by the statistically significant difference between the mean scores for experimental and control subjects, a high significant correlation between simultaneously measured scores by separate examiners, statistically significant correlations between subscores and total withdrawal scores for the narcotic-exposed experimental cases, and for this group, a statistically significant correlation between scores of withdrawal and the maternal dose of methadone. The simplicity of the NNWI should help to make it acceptable for use by physicians.