Eight Webb antigen Wb+ propositi, 2 in the same family, were found in testing 10,117 random blood donors in South Wales with anti-Wb serum. Family studies on the new propositi confirmed the Wb antigen to be inherited as an autosomal dominant character. Wb segregated independently from ABO, Rh, MNSs, K, Fy, Jk, and was not X- or Y-borne; for the first time Wb was shown to be independent of Lu. Wb antigen was destroyed by some proteolytic enzymes and by neuraminidase. Sera from 5,144 random donors were screened with Wb+ cells resulting in detection of 2 additional anti-Wb.