The 1991 International Yearbook of Nephrology is the third in a sueeessful .eries whieh has, as its principal aim, thc presentation of a eomprehensive list of topfes of the greatest current relevanee to elinieal nephrologists. We believe that, by following the subjeets eovered by the Yearbook in the broad field of nephrology, the praetieing nephrologist and nephrologist-in-training ean stay abreast of a number of rapidly advaneing fields. To improve the quality of the Yearbook, we have appointed an Editorial Board to provfde suggestions for topies and authors. Thus, we have invited 58 outstanding nephrologists from around the world (the list of them is included in this issue of the Yearbook) to identify annually potential topies for the Yearbook. The reply was exeel- lent and the contribution quite outstanding. Thus, for the 1992 Yearbook, we reeeived more than 150 suggestions. A number of them will be included in the next issue if they continue to be viewed as eurrent and important. We also invite readers to suggest topies for upeoming issues of the Yearbook. The present issue, the 1991 Yearbook, represents an improvement over previous volumes. We expeet this trend to be maintained in future years. As in previous issues, all ehapters provide a eomplete, aeeurate and up-to-date list of important references. We are grateful to all the authors for their exeellent eontributions and for having fulfilled the deadline in forwarding their manuseript. Our special thanks to Kluwer Aeademie Publishers for the timely publieation of this volume.