Upon infection, phage DNA is transported through the bacterial cytoplasmic membrane. This crossing is accompanied by a transient increase in the permeability of the cytoplasmic membrane toward ions and small solutes. This has led several authors to propose that DNA might cross the cytoplasmic membrane through channels. In the first part of the review we present data that we obtained with phage T4 and that strongly support this proposal. We then present the structural and ionic characteristics of these channels. In the second part, we summarize data obtained by several authors concerning the permeability changes induced by different phages and show that these results are compatible with a model of phage DNA transfer through channels. Finally, we discuss the possible origin of these channels.