The voltammetric behaviour of vitamin K-1 has been studied in aprotic media at cylindrical carbon fiber microelectrodes and Hg-coated microelectrodes. Cylindrical carbon fiber microelectrodes have proved to be effective supports in order to generate Hg-coated microelectrodes in non-aqueous media and these electrodes have turned out to be fit to perform voltammetric measurements in situ. The electroreduction of vitamin K-1 was found to be a two-step reaction at both types of microelectrode. The first electroreduction process involves a rapid (quasi-reversible) heterogeneous single-electron transfer and appears to be suitable for electroanalytical purposes.