Abstract: A method is disclosed for preparing a purified extraction residue fraction (antigen) of a microorganism isolated from the blood or urine of a warm-blooded animal or tumor carried by a warm-blooded animal, the microorganism having the capacity to synthesize the polypeptide hormone known as "chorionic gonadotropin" in its total form or in its alpha and beta subunits. The purified extraction residue fraction is an activator and modulator of immunological response and is capable of evoking pronounced prophylactic and therapeutic effects against a variety of tumors in laboratory animals and man. The immune response is stimulated by administering an effective immuno-stimulating amount of the residue fraction and/or co-administering the residue fraction together with an adjuvant such as the complete Freund's adjuvant.