Nongenomic actions of aldosterone have been described in a number of cell culture and in vivo systems. They occur, in contrast to the classical genomic effects on gene transcription, rapidly within seconds to minutes after aldosterone administration. The primary effector is still unknown. Whether it is a so far unidentified membrane bound aldosterone receptor or the classical mineralocorticoid receptor or both is under debate. The downstream signaling cascade involved in such rapid actions begins to be elucidated. In this work, we discuss the nature of the putative membrane receptor for aldosterone and summarize observed rapid aldosterone effects in different in vitro and in vivo systems.