Bacteriophages vB_EcoM-VR5, vB_EcoM-VR7 and vB_EcoM-VR20, showing an unusual low-temperature plating profile and producing constantly growing plaques, were isolated from aquatic environments of Lithuania. Although vB_EcoM-VR5, vB_EcoM-VR7 and vB_EcoM-VR20 resembled phage T4 both in their genome size and in their major structural protein (gp23) pattern, physiological properties of all three phages tested differed significantly from those of T4. With an optimum temperature for plating around 24 degrees C and a high efficiency of plating in the range 7-30 degrees C, bacteriophages vB_EcoM-VR7 and vB_EcoM-VR20 failed to plate at 37 degrees C, whereas phage vB_EcoM-VR5 could not be plated at 40 degrees C. Sequence analysis of diagnostic g23 PCR products revealed that g23 of vB_EcoM-VR5, vB_EcoM-VR7 and vB_EcoM-VR20 differed from the corresponding T4 g23 DNA sequence by 21, 21 and 20%, respectively.