Sensitivity and specificity of three reverse passive haemagglutination (RPHA) methods (Hepanosticon, Hepatest and Auscell) and of two solid‐phase radioimmunoassays (RIA) (Ausria‐125 and Ausria 11–125), all phase 3 tests for hepatitis B surface antigen (HBsAg), were compared with the sensitivity and specificity of an immunoelectroosmophoresis (IEOP) technique. By titration experiments the RPHA methods were shown to be 5–20 times more sensitive than the IEOP test, while RIA detected 5—10 times lower concentrations of antigen than the most sensitive RPHA test. In a study of sera drawn consecutively from patients with hepatitis B infections, the increased sensitivity of the test methods was according to the following order: IEOP, Hepanosticon, Hepatest, Ausria—125, Auscell, Ausria 11—125. There were significant differences between all the methods except for that between Ausria‐125 andAuscell. IEOP did not detect any false positives. If, however, RPHA tests were used, the incidence of nonspecific positive reactions would be in the range 0.5 per cent‐0.9 per cent. The advantages of the individual test meth