Sequences from the putative 5 nontranslated region of GB virus A were isolated from mystax, owl monkeys, and tamarins. Though sequences of isolates from each animal species are virtually identical at the nucleotide level (95%), isolates from different species are dramatically different (52 to 79% identical) and genetically cluster on this basis. The GB hepatitis agent was initially characterized in nonhuman primates inoculated with the blood serum of a 34-yearold surgeon experiencing acute clinical hepatitis (2). Following 12 serial animal passages, two distinct viral genomes were cloned from the serum of an animal with acute hepatitis (9). On the basis of genome size and organization, GB virus A (GBV-A) and GBV-B appear to be unique members of the Flaviviridae, most closely related to, but distinct from, the hepatitis C virus (HCV) group (4). Subsequent studies have demonstrated that GBV-B, in the absence of GBV-A, can induce hepatitis in the tamarin animal model (7). However, no significant elevations in serum liver enzyme levels were noted in tamarins singly inoculated with GBV-A, despite persistence of the virus in serum (7). Additionally, several animals were found to have a variant of GBV-A present in their serum prior to inoculation. Sequences within the putative 5Ј nontranslated region (NTR) of this variant were virtually identical to one another, though they were only 79% identical to those in the original GBV-A isolate (8). In the present study, we have identified GBV-A variants in mystax (GBV-A mx), owl monkeys (GBV-A tri), and tamarins (GBV-A lab) not known to have been inoculated with an infectious agent. These sequences are 52 to 79% identical at the nucleotide level to GBV-A and genetically cluster on the basis of the primate species from which they were isolated. Blood sera from Saguinus labiatus (tamarins), Saguinus mystax (mystax monkeys), and Aotus trivirgatus (owl monkeys) were used as source material for nucleic acids. Briefly, 25-to 50-l volumes were extracted with the DNA/RNA isolation kit (U.S. Biochemicals, Cleveland, Ohio) or the QIAamp HCV kit (Qiagen Inc., Chatsworth, Calif.). Random hexamer-primed nucleic acids were reversed transcribed as directed by the manufacturer with the RNA PCR kit (Perkin-Elmer, Foster City, Calif.) in a volume equal to that of the initial serum. Five microliters of the reverse transcription reaction mixture was used in a 25-l PCR mixture with 2.0 mM MgCl 2 and 0.5 M (each) oligonucleotide primer (8): 5ЈvA-s (5Ј-AGGGTTCGT AGGTGGTAAATCCC-3Ј) and 5ЈvA-a (5Ј-TGCCACCAGG GGTCACCCGAAG-3Ј). Amplification was performed by "touchdown" PCR (6) for 43 cycles (94ЊC
