A varphiX-specific DNA-protein complex has been isolated from varphiX-infected cells. This complex contains infective circular single-stranded DNA, the proteins of the genes F, G, H, and J in the same proportions as in the phage particle, and, in addition, the gene D-protein. The D-protein makes up 12-22% of the protein part of the complex. The sedimentation value of the complex is about 140 S. In vitro, the complex can be converted to the normal 114S phage particle (with a concomitant loss of its D-protein) or to an uninfective 70S particle and a small amount of free single-stranded DNA. The fast sedimenting particle is not associated with membranes.