Abstract The experiments described in this paper show the following: (1) Parental DNA of bacteriophage φX174 appears as an intact molecule in a newly synthesized protein coat among the progeny phage particles. (2) This transferred parental DNA has to pass through a double-stranded state, the parental replicative form DNA, before it is released into progeny particles. (3) Cytoplasmic parental replicative form DNA rather than the membrane-associated parental replicative form DNA is the precursor for the transferred DNA. (4) Single-stranded φX DNA free of coat protein can be detected in the host cell when the infection has been started in the absence of DNA synthesis. Normally, the parental single-stranded virus DNA is rapidly converted to a double-stranded replicative form DNA. (5) The super-infection exclusion phenomenon in φX-infected cells is probably based on alterations in the host cell surface.