A significant number of acute non A to E hepatitis cases are reported in Thailand every year, and the etiologies of these cases are unknown. Members of the herpesviridae family have been reported to cause either a self limited or fatal hepatitis in a small proportion of patients in other parts of the world. To determine whether herpesviruses may play a role in acute non A to E hepatitis, sera from 32 acute hepatitis patients without markers for acute hepatitis A to E virus infection were examined for IgM to herpesvirus type 2 (HSV-2), cytomegalovirus (CMV), and Epstein-Barr virus (EBV) using commercially available assays. IgM to HSV-2 was detected in four sera, IgM to CMV was detected in one serum, and IgM to EBV was detected in one serum. All of the acute non A to E hepatitis patients recovered and none had underlying conditions associated with impaired immunity. These results suggest that herpesviruses should be considered in the differential diagnosis for Thai patients with hepatitis.