By use of rate-zonal centrifugation, followed by either one-or two-dimensional agarose gel electrophoresis, the forms of intracellular bacteriophage T7 DNA produced by replication, recombination, and packaging have beep analyzed. Previous studies had shown that at least some intracellular DNA with sedimentation coefficients between 32S (the S value of mature T7 DNA) and 100S is concatemeric, i.e., linear and longer than mature T7 DNA. The analysis presented here confirmed that most of this DNA is linear, but also revealed a significant amount of circular DNA. The data suggest that these circles are produced during DNA packaging. It is proposed that circles are produced after a capsid has bound two sequential genomes in a concatemer. The size distribution of the linear, concatemeric DNA had peaks at the positions of dimeric and trimeric concatemers. Restriction endonuclease analysis revealed that most of the mature T7 DNA subunits of concatemers were joined left end to right end. However, these data also suggest that a comparatively small amount of left-end to left-end joining occurs, possibly by blunt-end ligation. A replicating form of T7 DNA that had .an S value greater than 100 (100S+ DNA) was also found to contain concatemers. However, some of the 100S' DNA,