Carboplatin is an alkylating agent that is FDA approved for the treatment of advanced ovarian cancer. Paclitaxel is a plant taxane mitotic inhibitor approved for primary or salvage treatment of ovarian and breast cancer. This is a case report of a 40-year-old woman who was exclusively breastfeeding prior to being treated for papillary thyroid cancer with intravenous carboplatin (233 mg) and intravenous paclitaxel (30 mg/m(2)) for 6 consecutive weeks. Breast milk samples were collected during the sixth chemotherapy session. Carboplatin had a relative infant dose of 2.0% and remained measurable after 316 hours. Paclitaxel had a relative infant dose of 16.7% but was eliminated before 316 hours. The potential side effects of infant exposure of these medications include myelosuppression, hypersensitivity reactions, nephrotoxicity, and neurotoxicity. It would be inadvisable for a mother to breastfeed while undergoing therapy with these 2 medications.