Coliphage T4D particles can attach not only to the cell surfaces of Escherichia coli B cells but also to the cell surfaces of mammalian cells. The adsorption of T4D phage particles was specific because their adsorptions was strongly blocked by N-acetyl-D-glucosamine and plant lectins such as concanavalin A and wheat germ agglutinin. Cytotoxic effects of bacteriocin(smegmatocin) derived from Mycobacterium smegmatis ATCC 14468 on simian virus 40-transformed BALB/c mouse tumor cells was inhibited by T4D phage particles. These results suggest the possibility that the receptors for coliphage T4D are shared by those for mycobacteriocin molecules on the cell membrane of the transformed cells.