The genetic variants of the coagulation factor XIIIB (FXIIIB) were analyzed by isoelectric focusing, carried out in agarose gels and followed by immunofixation. The FXIIIB phenotypes were visualized by a combined staining procedure with Coomassie Brilliant Blue R-250 and silver nitrate. Improved resolution was accomplished in polyacrylamide gels by hybrid isoelectric focusing in immobilized pH gradients supplemented with carrier ampholytes. We examined a total of 1,604 unrelated, healthy individuals from Southern Germany. The frequencies for the FXIIIB alleles were B*1 = 0.7581, B*2 = 0.0843, B*3 = 0.1568 and B*4 = 0.0019. The theoretical exclusion rate for disputed paternity is 22.35%.