The Cold Spring Harbor Laboratory is continuing its highly successful summer course in Advanced Bacterial Genetics. This course has its roots in the original Bacteriophage Course, initiated by Dr. Max Delbruck in 1945. This three week course prepares the participants to enter directly into research that requires advanced techniques and concepts in molecular genetics. Experiments providing a solid grounding in classical genetic analysis support training in contemporary uses of transposon mutagenesis, gene fusion technology, molecular cloning, site-directed mutagenesis and polymerase chain reaction as applied to diverse problems in bacterial and bacteriophage genetics. This course, which is unique in providing instruction in both genetics and molecular biology, gives participants the wherewithal required to perform analogous experiments in their home laboratories. The course instructors are chosen on the basis of their contributions to and knowledge of the field of bacterial genetics. Daily discussion periods cover the basis of the methodology used and fine points of experimental design and analysis. The course instructors invite guest lecturers to give up-to-the-minute reports on current research. Because the laboratory is always open, and because of the informal atmosphere, spontaneous discussions between participants, instructors, lecturers and laboratory staff occur regularly and at all hours. Course participants are chosen from a pool of highly qualified applicants ranging from graduate students to senior investigators.