The fourth edition of this volume in the Lecture Notes series has been rewritten to the point where it represents a new book more than a new edition. The text is aimed at senior undergraduate medical students and postgraduates in surgical and medical specialities. General pathology has been excluded on the grounds that the processes which constitute general pathology will have been studied at an earlier stage. Haematology is now a major subject in its own right, and whilst generally opposite aspects are incorporated in relevant organ systems, the more specific blood disorders are excluded. The considerable increase in knowledge of many disorders coupled with the decline of importance of some diseases has necessitated some considerable readjustment to the balance of the text and, to this end, a number of new contributers have been recruited. Strong emphasis is now placed on current trends and topics. The didactic approach of previous editions is retained as the layout making use of headings and sub-headings for clarity of presentation and ease of revision.