Limited information indicates that maternal cephalexin produces low levels in milk that are usually not expected to cause adverse effects in breastfed infants. Cephalexin is an alternative for the treatment of mastitis.[1,2] Occasionally disruption of the infant's gastrointestinal flora, resulting in diarrhea or thrush have been reported with cephalosporins, but these effects have not been adequately evaluated. A rare case of a severe allergic reaction occurred in an infant previously exposed to intravenous cefazolin whose mother began taking cephalexin while breastfeeding. Cephalexin is acceptable in nursing mothers.