The second edition differs from the first in many ways. Exercises 1 through 6 have been consolidated and streamlined. New procedures are used for large-scale plasmid isolation, yeast transformation, and DNA quantitation. New exercises have been introduced for polymerase chain reaction (PCR), for detecting/3- galactosidase in yeast colonies, for shuttling plasmids from S. cerevisiae to E. coli, and for detecting proteins on blots by antibod- ies. The Glossary has been amended and several new Appendixes have been added. For example, a new Appendix contains a list of World Wide Web addresses enabling students and instructors to access valuable information on the biological sciences on the Internet. All of the remaining Exercises and Appendixes have been completely revised to incorporate suggestions from students and instructors, and the references at the end of each exercise have been expanded, updated, and annotated.