Bacteriophage Hyø30 adsorbs only to the tip of the growing stalk and to the evolving daughter cell until a constriction in the stalk occurs and the daughter cell becomes flagellated. The motile, nondividing stage is immune to phage infection. Phage maturation was seen only in the daughter cell and stalk but was delayed or inhibited in the mother cell. It is suggested that a correlation exists between synthetically active cytoplasmic areas, receptor sites and phage replication.