Patients receiving kidney transplants (KT) are at high risk for blood borne viral infections. To determine the prevalence of a recently discovered hepatitis G virus (HGV) in this patient group, reverse transcription-polymerase chain reaction (RT-PCR) employing primers derived from the NS5 region of the viral genome was utilized. HGV RNA was detected in 40 of 94 KT patients (43%), as compared to 3 of 69 healthy subjects (4.3%). Cocirculation of HGV and hepatitis C virus (HCV) RNA was detected in 12 patients (13%). Comparison of patients with and without HGV revealed that the former had received hemodialysis before transplantation for a significantly longer duration than the latter (28 vs. 17 months, respectively; P < 0.05). The amount of blood transfused and mean levels of liver enzymes, including alkaline phosphatase, alanine transaminase, and aspartate transaminase, were the same in both groups. Sequence analysis of 275-base pair DNA clones obtained from 2 patients revealed approximately 92% sequence homology to the published HGV and GB virus C sequences. These results suggested that HGV infection among Thai KT patients was high and the role of HGV in causing liver disease remains to be determined.