DNA replication in eukaryotes is an important field, particular­ ly because of its direct impact on the study of cancer. The under­ standing of molecular mechanisms of replication and their regulation should allow a better comprehension of the alterations that lead to the proliferation of tumor cells and to error-prone repair in cells exposed to radiation or chemical carcinogens. During the last several years, many enzymes and proteins which participate in replication of DNA in eukaryotic cells have been identified, isolated and characterized. New concepts in chromatin structure have refocused attention on the study of replication of DNA complexed with his tones and non-histone chromosomal proteins. However, progress has been noticeably slower than for prokaryotes, essentially because of the difficulty in genetic analysis of eukaryo­ tic DNA replication. In June 1980, a workshop was organized in Cargese, Corsica (France) to facilitate exchanges of information between workers spe­ cializing in prokaryotes and those specializing in eukaryotes, and to allow discussion of new experimental approaches. With this in mind, special interest has been taken in the origin and termination of chromosome cycles and how they are controlled.