An active principle effective for control of the T-system of immunity, said active principle being obtained by removing thermolabile proteins from a solution of homogenized thymus gland tissue in a sodium chloride solution, precipitating proteins and peptides from the solution, dissolving the same in a solvent therefor, salting out the peptides from the solution, dissolving the peptides, subjecting the resulting solution to ultrafiltration, and subjecting the resulting ultrafiltrate to gel chromatography, and said active principle consisting of polypeptides with a molecular mass of from 1,500 to 6,000 Dalton, having the maximum of absorption in UV-light as 208 and 275 nm and the electrophoretic mobility in a polyacrylamide gel relative to bromophenol blue of:
- 0.062-0.102;
- 0.156-0.236;
- 0.354-0.374;
- 0.382-0.422;
- 0.432-0.472;
- 0.485-0.545;
- 0.850-0.930.