Reference and prototype strains of Streptococcus agalactiae (GBS) were originally selected on the basis of phenotypic traits which, however, do not always mirror genotypic traits. A total of 14 reference and prototype GBS strains were examined by PCR designed to detect the bca and beta genes, encoding the c proteins c(alpha) and c(beta), respectively. The cognate proteins were detected by whole-cell-based fluorescent antibody testing and Western blotting. The PCR for beta gene detection and the antibody-based c(beta) protein detection showed concordant results with all of the isolates, whereas 7 of 14 strains which did not express c(alpha) protein at detectable levels contained bca gene elements, consistent with bca gene and gene product divergency in these strains. The results emphasize the importance of genetic characterization of reference and prototype strains of GBS which, in the past, have been selected on the basis of phenotypic traits.