cDNA probes specific for the alpha, beta and gamma subunits of human C8 were used to establish that genes encoding alpha and beta are physically linked and in a 5' alpha-beta 3' orientation on chromosome 1. The gene encoding the gamma subunit was mapped to chromosome 9q. These results explain the close genetic linkage between alpha-gamma and beta on chromosome 1 and indicate that alpha-gamma polymorphisms detected in earlier genetic studies are determined solely by alpha. Results summarized in this report were presented at the VIth Complement Genetics Workshop and Conference (Mainz, FRG, 1989).