Hepatitis B virus infection is responsible for both morbidity and mortality in kidney transplant recipients. Adenine arabinoside 5'-monophosphate (ARA-AMP), a synthetic purine nucleotide with anti-viral activity, leads to a sustained interruption of HBV replication in approximately 40% of immunocompetent patients. We report the results of a pilot study using ARA-AMP to treat HBV-related chronic active hepatitis in kidney transplant recipients. Ten patients (2 females and 8 males, mean age 44 years, mean time post-transplantation 163 months) received a 28-day course of ARA-AMP intramuscularly: 5 mg/kg twice daily for the first 5 days during hospitalization and subsequently 5 mg/kg once daily at home for the remaining 23 days. Mean follow-up was 18 months, ranging from 7 to 28 months. All patients but one had biopsy-proven chronic hepatitis, including five cases of cirrhosis. All patients had been chronic HBs Ag carriers for more than 1 year and had active replication as assessed by the presence of serum HBV DNA (mean titre, 270 pg/ml, ranging from 12 to 997 pg/ml, Genostics method). HBe Ag was present in 7 of the 10 patients. Pretreatment creatinine was normal. In four of the 10 patients, HBV DNA became undetectable respectively 1, 1, 5, and 11 months after beginning ARA-AMP. In five patients, HBV DNA decreased during ARA-AMP therapy but subsequently increased although no change was noted during the follow-up period.(ABSTRACT TRUNCATED AT 250 WORDS)