FromEnterococcus faecalis cells containing random chromosomal insertions of Tn916, strains resistant to a lytic phage were selected and tested for conjugal mating ability. The phageresistant strains all showed decreased recipient ability (Con-) in broth matings with donors carrying pheromone-inducible plasmids. These strains were normal with respect to donor ability in broth matings and recipient ability in filter matings. The data suggest that the mutants are deficient in the binding substance receptor for the pheromone-induced donor aggregation substance. These mutants contained multiple insertions of Tn916, and none of the individual insertions from the mutant strains were capable of generating the phenotype. Analysis of cell envelope lipoteichoic acids and protein revealed changes in both associated with the Con- phenotype.