This book is based on practical experience and is therefore written as a prac­ tical manual. The fore-runners of the book were the manuals of the first and second EMBO-Courses on "Micromethods in Molecular Biology" which were held in G6ttingen in the spring of 1970 and the autumn of 1971. This book may serve as a manual not only for the participants of the third EMBO-Course to be held in G6ttingen in autumn 1973, but also for all experimenters who are interested in using micromethods. It must be emphasized from the outset that this book is conceived as a "cook book" and not as a monograph which attempts to revue the literature on micromethods critically. The methods described here in detail are performed routinely in the authors' laboratories and include all the practical details necessary for the successful appli­ cation of the micromethods. There are many other sensitive and excellent micro­ methods which are not included in this book, because the authors feel that in a "cook book" only methods for which they have personal experience and profi­ ciency should be described. Some readers may feel that the title promises more than the present contents of this book; however, if sufficient interest is shown in this volume, it may be possible to remedy such deficiencies in future editions.