Chromosome transfer during conjugation by an induced Hfr lysogenic for a thermoinducible lambda mutant has been used to investigate prophage excision and chromosome healing following induction. The results show that transient heat induction leads to prophage excision and chromosome healing before the cells are induced to produce phage yield. These processes take place early after induction and are not affected by mutations in genes O or P. No detachment is observed in lysogens carrying mutations in the N or int genes.