Abstract: A method is disclosed for the treatment of hepadnavirus infection in animals. Animals infected with duck hepatitis B virus may be treated with the 2',3'-dideoxynucleoside of adenine, guanine, hypoxanthine, 2,6-diaminopurine or various analogs of substituted purines. Several purine 2',3'-dideoxynucleosides inhibit duck hepatitis B virus in hepatocyte culture >99% at 1 .mu.g/ml. Potent in vivo efficacy of the 2,6-diaminopurine 2',3'-dideoxynucleoside for clearance of duck hepatitis B virus from the sera of Pekin ducks is demonstrated. The selective effect on hepadnavirus replication by the purine 2',3'-dideoxynucleosides is based on the discovery of an unexpected sensitivity of hepadnavirus to purine 2',3'-dideoxynucleoside analogs. These compounds present a new antiviral therapy of acute or persistent hepadnavirus infections.