Phage-associated enzymes which act on capsules of hosts with the production of plaques surrounded by halos have been reported for a number of capsulated Gramnegative bacteria (Bartell, Orr & Lam, 1966; Chakrabarty, Niblack & Gunsalus, 1967). Organisms in the halos are devoid of capsules but are viable and in some instances become sensitive to the action of different phages. This suggests that hidden phage receptors may have been exposed (Sutherland & Wilkinson, 1965). This communication describes the isolation and action of a capsule-depolymerizing enzyme associated with an Alcaligenes faecalis phage host system.