Involvement of UV-inducible protein(s) in repair of various E. coli K-12 cell strains has been investigated using a procedure of double UV irradiation and postincubation with chloramphenicol. From the course of dose survival curves the following conclusions concerning significance of a UV-inducible protein have been drawn: 1. It is a very important for wild type cells; in these cells its early occurrence is necessary to prevent killing. 2. It is involved in repair of excision-deficient cells; however, its action early after UV is less urgent. 3. It is not involved at all in repair of lex mutant cells; 4. It exhibits some effect on survival of recA as well as recB mutant cells. We conclude that the protein is involved in excision repair as well as in resumption of DNA replication.