The transport and accumulation of K+ in higher plant roots is regulated by ABA. Molecular and electrophysiological techniques have identified a number of discrete transporters which are involved in the translocation of K+ from the soil solution to the shoots of higher plants. Furthermore, recent reports have shown that ABA regulates K+ channel activity in maize and Arabidopsis roots which suggests that ABA regulation of K+ transport in roots is, at least in part, ion channel-mediated. The signalling processes which underlie the ABA regulation of K+ channels have been investigated. The effects of ABA on the membrane potential of intact maize root cells were also studied. It was found that ABA regulated the membrane potential of root cells and that this regulation is consistent with the hypothesis that ABA-induced K+ accumulation in roots is mediated by K+ channels.