Methadone is a drug that is commonly used to treat opiate addiction, usually as part of a detoxification and maintenance program. Methadone offers significant therapeutic benefits to pregnant women who are opiate dependent, and it is currently the treatment of choice for this group of people. In general, breast milk is beneficial for infants. However, there is some concern as to whether it is safe for women who are taking methadone to breastfeed their babies. The purpose of this study is to determine the amount of methadone in the breast milk of women who are breastfeeding and taking methadone for opiate addiction. In addition, this study will evaluate the effects of methadone on infant neurobehavior.