We describe a solid-phase radioimmunoassay, based on the "sandwich" principle, using anti-HBe1/anti-HBe2 containing IgG precoated to polystirene beads as the solid-phase, and 125I-anti-HBE as labelled antibody for the detection of HBeAg and a two steps competitive procedure for the detection of anti-HBe. Comparison of titre obtained by ID and RIA or reference sera containing HBeAg and anti-HBe revealed that RIA is about 200 fold more sensitive than ID in detecting both HBeAg and anti-HBe. Moreover an increase in the detection rate of HBeAg from 5.9% (ID) to 15% (RIA) and of anti-HBe from 47.8% (ID) to 74.2% (RIA) and consequently a reduction of the frequency of negative samples for both HBeAg and anti-HBe from 46.3% (ID) to 10.8% (RIA) was determined by testing sera from HBsAg asymptomatic carriers. With regard to specificity, the frequency of presumptive HBeAg positive samples not confirmed was of 1 out of 29 (3.4%). Technical improvements of sensitivity and specificity of the described RIA are under development.