Herpesviruses are associated with several diseases of marine turtles including lung-eye-trachea disease (LETD) and gray patch disease (GPD) of green turtles (Chelonia mydas) and fibropapillomatosis (FP) of green, loggerhead (Caretta caretta), and olive ridley turtles (Lepidochelys olivacea). The stability of chelonian herpesviruses in the marine environment, which may influence transmission, has not been previously studied. In these experiments, LETD-associated herpesvirus (LETV) was used as a model chelonian herpesvirus to test viral infectivity after exposure to seawater. The LETV virus preparations grown in terrapene heart (TH-1) cells were dialyzed for 24 to 120 hr against aerated artificial or natural sea-water or Hank's balanced salt solution (HBBS). Fresh TH-1 cells were inoculated with dialyzed LETV, and on day 10 post-infection cells were scored for cytopathic effect. Virus samples dialyzed up to 120 hr were positive for the herpesvirus DNA polymerase gene by polymerase chain reaction. Electron microscopy revealed intact LETV nucleocapsids after exposure of LETV to artificial seawater or HBSS for 24 hr at 23 C. LETV preparations remained infectious as long as 120 hr in natural and artificial seawater at 23 C. Similar results were obtained with a second culturable chelonian herpesvirus, HV2245. LETV infectivity could not be detected after 48 hr exposure to artificial seawater at 30 C. Since LETV and HV2245 remain infectious for extended periods of time in the marine environment, it is possible that FP-associated and GPD-associated herpesviruses also may be stable. These findings are significant both for researchers studying the epidemiological association of herpesviruses with diseases of marine turtles and for individuals who handle turtles in marine turtle conservation efforts.