Electrophoretic mobilities of three hemoglobins (Hb1, Hb2, and Hb3) were studied in 15 populations of brine shrimps. Genetic segregation data support the model that Hb2 contains n alpha-polypeptides and n beta-polypeptides; Hb1 contains 2n alpha-polypeptides- Hb3 contains neither alpha- nor beta-polypeptides. There is no evidence of linkage of alpha and beta loci with each other or with the locus (or loci) which governs Hb3 or with the nonhomologous portion of the sex chromosomes. Hemoglobins of different populations may be hybridized in vitro by incubation at high temperature. Reversible dissociation to subunits which contain only one (alpha or beta) polypeptide occurs at 40 C (for Hb1) and at 50 C (for Hb2).