Twenty-two heterosexuals and 21 homosexuals with chronic active hepatitis B and who had HBsAg, HBeAg and hepatitis B virus DNA in serum were randomized separately to receive adenine arabinoside monophosphate or placebo. In the 10 heterosexuals and nine homosexuals who received placebo, no change in hepatitis B virus DNA level and HBeAg was observed. Among the patients who received adenine arabinoside monophosphate, seven of the 12 heterosexuals and five of the 12 homosexuals lost hepatitis B virus DNA; five heterosexuals and three homosexuals also lost HBeAg; one homosexual lost HBsAg. There was no significant differences in response between heterosexual and homosexual patients. When results were pooled, there was a significant effect of adenine arabinoside monophosphate on hepatitis B virus replication. None of the 19 patients who received placebo but 50% of the 24 patients who received adenine arabinoside monophosphate were negative for serum hepatitis B virus DNA at 10 months after treatment (p less than 0.001) and none of the 19 patients who received placebo and 33% of the 24 patients who received adenine arabinoside monophosphate were negative for HBeAg in serum (p less than 0.005). Retrospective analysis showed that disappearance of hepatitis B virus DNA after administration of adenine arabinoside monophosphate was more common (i) in patients with a low pretreatment hepatitis B virus DNA level than in patients with a high pretreatment hepatitis B virus DNA level (8/11 vs. 4/13, p less than 0.05); (ii) in patients with a high pretreatment ALT level than in patients with a low pretreatment ALT level (10/14 vs. 2/10, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)