By means of alloimmunization of mink, two new antigens, Lpm-7 and Lpm-8, were detected in their sera. Lpm-7 and Lpm-8 allospecificities were referred to a very high density alpha2-lipoprotein (Lpm) by the following criteria: histochemical tests, immunoelectrophoresis, preparative ultracentrifugation, and coalescence of alloprecipitates with heteroprecipitates in double diffusion tests. Genetic analysis indicated that Lpm-7 and Lpm-8, together with the earlier described Lpm-1, Lpm-2, Lpm-3, Lpm-4, and Lpm-5, share a common immunogenetic system. Polymorphism for the seven markers is conditioned by the genetic units Lpm8, Lpm4, Lpm4,8, Lpm4,7, Lpm3,4,8, Lpm1,8, Lpm1,2,7, and Lpm2,4,5,7, which behave as alleles. Of these units, the latter six are probably haploid sets of closely linked genes.