Enterovirus 70 isolates obtained in Asia and the Americas between 1980 and 1981 from cases of acute hemorrhagic conjunctivitis were found to be very closely related by RNase T1 oligonucleotide fingerprinting. Two closely related isolates from the first acute hemorrhagic conjunctivitis epidemic (1969 to 1972) differed by many oligonucleotides from the 1980 to 1981 pandemic strains. The strong similarities of oligonucleotide patterns of isolates from the same epidemic but from distant regions of the world suggest that the genome of enterovirus 70 tends to be conserved during natural infection, a possible consequence of the transient nature of the disease.