in a method of treating viral infections and of tumors induced thereby a radioimmunoconjugate containing an immunologically effective component and a radioactive component is provided . the immunologically effective component contains a ) a receptor molecule or a fragment thereof having affinity to an epitope of the viral structural proteins expressed on the plasma membrane of infected cells , or b ) a fragment of the cellular receptor molecule modified by mutagenesis , the fragment having affinity to an epitope of the viral structural proteins expressed on the plasma membrane of infected cells . the radioactive component is an alpha emitter or a beta emitter . the therapeutical agent is effective against viral infections such as hiv , hbv , hcv , hdv , htlv , cmv , ebv , or hhv8 infections .