An alpha-herpesvirus has been associated recently with green turtle fibropapilloma (FP). To further clarify the role of this newfound green turtle herpesvirus (GTHV) in the pathogenesis of FP, various normal-appearing tissues and organs (including skin, eye, brain, heart, liver, spleen, intestine, lung, kidney, nerve, gonad, tongue, gall bladder, urinary bladder, thyroid and peripheral blood mononuclear cells (PBMC) from blood) and tumor tissues from 19 green turtles (Chelonia mydas) with FP, and tissues from three green turtles without FP, collected during 1997 to 1999 in the Hawaiian Islands, were tested for GTHV sequences by nested polymerase chain reaction (PCR), using GTHV-specific oligonuclotide primers. GTHV sequences were detected in all tumors (51/51) and most tissues (133/167) of tumored turtles. By contrast, such sequences were undetectable in tissues (0/28) of three non-tumored turtles. Analysis of GTHV sequences detected in different tissues and tumors revealed a low degree of genetic diversity (<1%). The wide distribution of this newfound herpesvirus in tumors and tissues of tumored green turtles and its absence in tissues of non-tumored turtles, argues for an etiologic role in FP.