AbstractTransferable productive lysis in stable protoplast type L‐form cells ofBacillus subtiliswas producted by 6 phages out of 14 strains virulent for the parentB. subtilis170 and 1997. Most of these Phages lytie for L‐forms show the ϕ 29 morphology characteristic for the smallestB. subtilisPhages containing double‐stranded DNA. Among 31 actinophages, 23 of which were virulent forStreptomyces hygroscopicus, only SLE 109 and ϕc 31 gave productive infection of the stable protoplast type L‐form ofS. hygroscopicusNG 33–354.Electron microscopic investigation and treatment by DNAse demonstrated that infection of L‐forms cells is an adsorption‐injection process, and that it is not caused by transfection of free phage DNA or endocytotic uptake of phage particles. Because in both stable L‐forms cell wall biosyntheesis blocked irreversibly the results allow the conclusion that specific receptors must be localized in the cyroplasmic membrane for those phages producing transferable lysis in protoplast type L‐forms. Localization of receptors for certain phages in the cytoplasmic membrane seems to occur in many Gram‐positive bacteria, but not in G