The material in this text was compiled to serve as a study guide for a review of microbiology and immunology suitable for preparing for Part I of the National Board of Medical Examiners (NBME) exam. I have assumed that you, the reader, have had a comprehensive course covering this discipline. In-depth presentation of material will not be found in this review: You are urged to consult other study aids (lecture notes, textbooks, etc.) for detailed explana tions of material that you find troublesome. In general, the text of the book is on the left side of each page; questions, illustrations, summary sentences or phrases, and other study aids are on the right. This format has the intent of getting you involved in the review process. Use a highlighter, put boxes around key statements, answer the questions, and fill in the blanks as you work through the book. Your reward will be proportional to your effort (i.e., no pain, no gain). There are five proficiency examinations in this book, one for each major area of coverage. In addition, a comprehensive examination will be found at the end of the book. Performance data for each is given to help you evaluate your own preparedness. Some questions may cover material not detailed in the book: Be sure that you know the answer to these questions as well, since this is just another form of review.