We have analyzed the structure of visna virus DNA synthesized during the life cycle of this lytic virus in confluent cultures of sheep choroid plexus cells. Viral DNA is of predominantly two forms: A linear duplex of about 6 million daltons corresponding to a transcript of viral RNA of subunit size; and, a structure with a gap in the center comprised of a full-length minus strand, and two long plus strands that together are about 300-500 bases shorter than the minus strand. A physical map of the linear DNA derived with restriction enzymes was ordered with respect to viral RNA, and the DNA was shown to bear terminal repeats of 350-450 nucleotides. Two circular forms of visna DNA differing only by the length of one terminal repeat also were detected, but constituted a very minor population. We discuss the relationship of these observations with this prototype of the lentiviruses to those recorded for transforming retroviruses.