The detection of the HB'S Antigen by a reversed passive haemagglutination test (Hépanosticon) in sera previously heated at 56 degrees C for 30 mn, is simple and rapid but gives a relatively high number of false positive results. A simple technique is suggested by heating sera betwen 68 degrees C and 80 degrees C and then by centrifugation at 1.500 g for 15 mn, to eliminate these false positive results. The supernatants are tested in the Hepanosticon technique and only the true positive samples, cheked for specificity by other techniques namely radioimmuno assay (R.I.A.) remain positive. Further research is pursued to confirm these first data and to define the exact degree of sensibility of this technique.