  We propose a new method of direct detection of spin accumulation, which
overcomes problems of previous measurement schemes. A spin dependent current in
a single-electron transistor with ferromagnetic electrodes leads to spin
accumulation on the metallic island. The resulting spin-splitting of the
electrochemical potentials of the island, because of an additional shift by the
charging energy, can be detected from the spacing between two resonances in the
current-voltage characteristics. The results were obtained in the framework of
a real-time diagrammatic approach which allows to study higher order
(co-)tunneling processes in the strong nonequlibrium situation.
