There is an article titled "Exposure of Young Infants to Environmental
Tobacco Smoke:  Breast-Feeding among Smoking Mothers"  in the June
issue of the Am. J. of Public Health (Vol. 88, pages 893-896).  Their
reasearch suggests that breastfeeding, rather than inhaling
environmental tobacco smoke, is the primary determinant of cotinine
levels in babies whose mothers smoke.  These authors conclude that
"health care providers need to be as diligent in encouraging mothers to
stop smoking after birth as in the prenatal period", and there is no
implication made that it would be better not to breastfeed.
Susan MacDowell, MPH, RD, CLE, Cincinnati