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Three minor forms of renin from the submaxillary glands of male mice called D1, D2, and E have been purified to homogeneity. Their amino acid compositions are identical to the principal form of mouse submaxillary gland renin (renin A), except for 1, 1, and 2 extra arginine residues, respectively. The electrophoretic mobility of renin D2 does not change upon reduction, indicating that its heavy and light chains are linked by more than a disulfide bond. The light chain of renin D1 has an electrophoretic mobility different from the light chain of renin A. Renin D2 is proposed to be renin A with an arginine-arginine dipeptide connecting the carboxyl terminus of the heavy chain to the NH2 terminus of the light chain, with the light chain missing the carboxyl-terminal arginine of renin A. Renin D1 is suggested to be renin D2 with the peptide bond between an arginine and the NH2 terminus of the light chain cleaved. Renin E is proposed to be renin D1 plus the carboxyl-terminal arginine of the light chain. A fourth minor form of male mouse submaxillary renin, called renin B/A, has been purified to homogeneity in sodium dodecyl sulfate-polyacrylamide gel electrophoresis and in isoelectric focusing. Renin B/A seems to be a second renin gene product which is difficult to separate from renin A. Renin B/A has an amino acid composition significantly different from renin A, and all three preparations of B/A had compositions significantly different from one another. For renin B/A, the light chain sequence and the first 53 NH2-terminal residues of its heavy chain sequence were identical to renin A.