Factor B (BF) reference typing was carried out on the occasion of the VIIth Complement Genetics Workshop in Mainz, May 1998. Two different sets of samples were analysed by agarose electrophoresis and/or isoelectric focusing at the protein level, and by PCR-RFLP analysis at the DNA level. These results confirmed the reliability of the standard agarose electrophoresis technique for the identification of the major BF alleles as well as for the identification of cathodic and anodic variants. However, the exact alphanumeric designation of individual variants relative to the reference distance between alleles S and F1 turned out to be more difficult. Using PCR-RFLP analysis, the common alleles F and S as well as the FA and FB subtypes in 6 samples containing an F allele were all assigned correctly. However, the variants F1 and S07 were not detected by this method, as they could not be distinguished from the accompanying S allele. Therefore, a combined application of all three typing methods is recommended for a reliable identification of factor B alleles, variants and FA/FB subtypes.