Trastuzumab, a humanised monoclonal antibody directed against the extracellular domain of HER-2, has been shown to be active against HER-2-overexpressing metastatic breast cancer, either as single agent or when used in combination with chemotherapy. In preclinical models, trastuzumab has shown additive and even synergistic anti-tumour activity with the most active chemotherapeutic agents used in the treatment of breast cancer. In a large, randomised, Phase III trial, the combination of trastuzumab plus chemotherapy was shown to improve response rate and survival. The high incidence of cardiotoxicity seen with the combination of trastuzumab plus anthracycline drugs prompted carrying out of several clinical studies combining trastuzumab with other chemotherapeutic agents, including docetaxel, vinorelbine, platinum salts, gemcitabine and capecitabine. This article summarises the available data on trastuzumab-based combinations for breast cancer.