Electronmicroscopic observations indicate that bacteriophage CVX-5 has an angular head with long spiral tail which is noncontractile, possibly having 2--3 tail fibres attached at the distal part of the tail. This phage is antigenically unrelated to any of the T-phages. Inhibition of phage CVX-5 multiplication by mitomycin C and incorporation of 3H-thymidine into this phage indicate that phage CVX-5 is a DNA phage.