The objective of this proposed study is to determine the primary structure of Lumbricus extracellular hemoglobin. This giant molecule possesses a molecular mass of 3.9 million x 10 to the 6 and contains about 160 heme groups. Its quaternary structure in electron micrography is that of a hexagonal bilayer of twelve spherical subunits with an empty central circurity. The Lumbricus molecule consists of at least six polypeptide chains, four having molecular masses from 16,000 to 19,000 and two having Mr = 31,000 and Mr = 37,000. These chains have been separated by gel filtration and ion exchange chromatography and extensive preliminary data on the amino acid sequence of the smallest chain has already been obtained. In addition, we intend to characterize partially the primary structures of several other annelid extracellular hemoglobins; those of another oligochaete (Tubifex) and three polychaetes (Arenicola, Auphitrite and Nephtys). Although Lumbricus and Arenicola hemoglobins possess the same dimensions, the latter is built of only two polypeptide chains of 16,000. Tubifex hemoglobin possesses a smaller molecular mass and dimensions than the other molecules and is composed of one chain of about 16,000. The stability of the Amphitrite hemoglobin is strongly cation concentration dependent, and Nephtys hemoglobin, although it possesses the same dimensions as the other hemoglobins, has an additional subunit within its central cavity. The acquisition of information about the amino acid sequences of the constituent polypeptide chains of these hemoglobins is a prerequisite for understanding their mode of aggregation and functional differences.