The material in this text was compiled to serve as a study guide for a REVIEW of microbiology and immunology suitable for preparing for Step 1 of the United States Medical Licensing Examination (USMLE). I have assumed that you, the reader, have already had a full fledged course covering this discipline. In-depth presentation of material will not be found in this review. You are urged to con sult other study aids (lecture notes, textbooks, etc. ) for detailed explanations 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). As the format is a work book, you benefit most by active participation. Write key words in the margins; add to the Review State ments by writing out your own; use whatever study skills you have found help you "master" an area.