Tamoxifen protects membranes and lipoprotein particles against oxidative damage. This antioxidant action is likely to contribute to the observed cardioprotective action of tamoxifen and supports the use of this compound in treating and even preventing breast cancer. Membrane-mediated mechanisms of tamoxifen action, through a putative modulation of membrane fluidity, are likely to play an important role in its anticancer action and its ability to reverse multidrug resistance, and could also lead to clinical uses as an anti-Candida and anti-viral agent. In this review, Helen Wiseman discusses the interaction of tamoxifen with membranes and lipoprotein particles, and considers the possible clinical implications.