Cleavage of adenovirus-associated virus type 2 (AAV2) DNA linear duplex monomers with the restriction endonuclease R-EcoRI yielded three fragments, A, B, and C, having approximate mol wt of 1.6 X 10(6), 1.1 X 10(6), and 1.3 X 10(5), respectively. Radioactive labeling the 5' termini of AAV DNA before cleavage with R-EcoRI showed that A and B were terminal fragments and C was internal. Separation of the complementary strands of fragments A and B showed that A contained the 5' terminus of the minus strand and the 3' terminus of the plus strand, and conversely for fragment B. The physical map of the AAV R-EcoRI fragments can thus be unambiguously determined and is drawn with B at the left-hand and A at the right-hand end. On this map, transcription of stable AAV mRNA from the minus strand proceeds from left to right, beginning in fragment B and terminating in fragment A. The asymmetry in distribution of thymidine between the AAV DNA plus and minus strands is preferentially located in fragment A, which represents the right-hand half of the duplex molecule. These experiments enable preparative separation of all four single-strand termini of AAV DNA and provide a basis for orientation of fragment maps derived by cleavage with other restriction enzymes.