We propose: (i) investigations of Cassel's 73-T, an Ehrlich's mouse ascites carcinoma-adapted Newcastle disease virus (NDV) strain that so effectively reduced relapse rates in malignant melanoma if it is an admixture or a recombinant with a murine parvovirus; (ii) transfection of prostatic carcinoma cells with the TRMP gene; (iii) transfection of sarcoma cells with the fas gene followed by treatment with anti-fas monoclonal antibodies, and (iv) treatment of metastatic tumors with a parvovirus incorporating the apoptosis-inducer Ad5 E1A gene.Thus, replicating virions and haphazard generation of cytokines in the inoculated host could be replaced with transfection of single genes of well-defined, limited but selected efficacy.