The C 3 polymorphism was studied by agarose gel electrophoresis in a series of serum samples from 148 Swedish Lapps. The frequencies of the genes C31 and C32 were estimated to be 0.027 and 0.973, respectively. The distribution of C 3 phenotypes in Swedish Lapps was significantly different from that among Swedes. Reexaminations of certain sera indicated that the previously described phenotype 2–4 may be a storage artefact.