Fourteen young Chinese marmots (Marmota bobak sibirica Radde) were randomly allocated to two groups of seven each. They were injected intrahepatically with a standard woodchuck hepatitis virus challenge pool or a negative pool, prepared from sera of woodchucks with and without woodchuck hepatitis virus infection, respectively. Marmot No. 2 in the experimental group experienced an episode of seroconversion from woodchuck hepatitis surface antigen to anti-woodchuck hepatitis antibody. Woodchuck hepatitis virus DNA was detected, and woodchuck hepatitis surface antigen particles of both spherical and filamentous forms and intact woodchuck hepatitis virus virions were found in its serum. By contrast, none of the control group animals (receiving the negative pool) produced any marker of woodchuck hepatitis virus. This suggests that young Chinese marmots can get woodchuck hepatitis virus infection.