The antitumor and immunoadjuvant action of water-soluble N-vinylpyrrolidone co(ter)polymers of different chemical structure is studied. It is established that terpolymer N-vinyl-pyrrolidone (VP)--crotonic acid (CA)--n-crotonoylaminophenol inhibiting the growth of hepatoma 22a by 50-60% possesses an antitumoral action, while copolymer VP-CA has an immunoadjuvant action. These properties of co(ter)polymers are due to their chemical structure and molecular weight, but they do not always correlate between themselves.