A new B locus antigen has been found in members of two unrelated families and in a patient originating from Morocco belonging to the Berber population. A complete analysis has been performed with antisera from the 9th and 10th IHWS defining the B5 CREG antigens. Serology, absorption experiments and family studies indicate that SNA antigen is a Bw6 associated subtype of B5 antigen closely related to but clearly distinct from each of the B5 CREG antigens. One-dimensional isoelectric focusing study (1D-IEF) confirms that the SNA antigen precipitates as a B locus gene product and has an isoelectric point identical to that of Bw52 and one of the charge variants of B51.