Dr. Hale's comments about I-131 were greatly appreciated. On reviewing the basis for my previous comments, the AAP Statement in Pediatrics Jan. 1994, I noted that their figure of 2-14 days of presence of radioactivity in milk was based on studies which were old (1950's and '60's), and although I have not reviewed them, the titles suggest use of I-131 in diagnostic studies, presumably using a much lower dose than that required for ablation of the thyroid gland. My apologies for quoting these figures without reviewing their sources. I still don't see any evidence that the issue of potential breast cancer in the lactating breast after I-131 exposure has been studied, but this may be a moot point if the length of time for breastfeeding cessation is so long that a return to breastfeeding is unlikely. Since there are two other alternatives as treatment for Graves' disease, i.e. medical therapy with PTU (compatible with breastfeeding) or surgical excision of the thyroid, I would think that those two options would be preferable to a mother who wishes to continue breastfeeding. While on the subject of Graves' disease, I currently have a patient at 32 weeks gestation who has had Graves' for years and has been suppressed with PTU. The plan is to continue PTU while breastfeeding. Her endocrinologist recently did a thyroid stimulating immunoglobulin test on her, which was high and suggests a significant risk of neonatal thyrotoxicosis in her baby. I looked up what if any relevance this may have on her breastfeeding, and the only reference that addressed this was Ruth Lawrence in Medical Clinics of North America sometime in 1989 (the reference is not handy, but I can get it for anyone who requests it). She suggested that little of this immunoglobulin gets absorbed in baby's GI tract, and that no increased risk of neonatal thyrotoxicosis was found. Does anyone know of any other references about this? Thanks, Alicia. [log in to unmask]