Pulsed field electrophoresis established that Chlorella viruses contain linear, nonpermuted, 330- to 380-kb dsDNA genomes. Terminal DNA restriction fragments of one virus, PBCV-1, were identified by Bal31 exonuclease digestion; the termini probably contain covalently closed hairpin ends. The end fragments cross-hybridize indicating terminal repetition; the region of repetition extends no more than 2.5 kb from the ends.