The influence of rifampicin, streptolydigin, tetracycline, and chloramphenicol on phage DNA transport from the T7 virion into the E. coli cell was studied. It has been found that the DNA transport proceeds in at least three stages. During the initial stage the phage injects into the host cell the left 10 per cent of its DNA molecule. The entrance of the next 50 per cent of T7 DNA molecule is blocked by inhibitors which block transcription but not translation. Moreover, the entrance time of this part of the T7 DNA increases in the case of the T7 mutant D11 (which contains a deletion of the A2and A3promoters) and decreases in the case of the D53 mutant (which containsa deletion in the region of the early gene transcription terminator). It would appear, that the second stage of the phage DNA transport is tightly coupled with its transcription and that a mechanical function is carried out by RNA polymerase. The translation inhibitors completely block the entrance of the remaining 40 per cent of the T7 DNA molecule (class III genes) into the host cell. It would appear that some class I and (or) II gene product(s) are obligatory components of the final stage of T7 DNA transport. Some probable consequences of this virus DNA transport model as well as its agreement with the functional structure of T7 chromosome and with T7 development are discussed. © 1982 IRL Press Limited.