An increasing number of ion channels are being found to be causally involved in diseases, giving rise to the new field of "channelopathies". Cancer is no exception, and several ion channels have been linked to tumour progression. Among them is the potassium channel EAG (Ether-a-go-go). Over 75% of tumours have been tested positive using a monoclonal antibody specific for EAG, while inhibition of this channel decreased the proliferation of EAG expressing cells. The inhibition of EAG is accomplished using RNA interference, functional anti-EAG1 antibodies, or (unspecific) EAG channel blockers. Fluorescently labelled recombinant Fab fragments recognizing EAG allow the distribution of EAG to be visualized in an in vivo mouse tumour model.